Devices and Methods for Treatment of Facet and Other Joints

ABSTRACT

Embodiments of the present invention describe methods, devices and instruments for resurfacing or replacing facet joints, uncovertebral joints and costovertebral joints. The joints can be prepared by smoothing the articular surface on one side, by distracting the joint and by implant insertion. Implants can be stabilized against a first articular surface by creating a high level of conformance with said first articular surface, while smoothing the second articular surface with a surgical instrument with a smooth mating implant surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application claims the benefit of U.S. provisional patentapplication 61/052,468 filed on May 12, 2008, entitled “Treatment ofFacet Joint Disease”, which is incorporated herein by reference in itsentirety.

The current application is also a continuation-in-part of U.S. patentapplication Ser. No. 11/602,713 filed Nov. 21, 2006 and entitled“Devices and Methods for Treating Facet Joints, Uncovertebral Joints,Costovertebral Joints and Other Joints,” which claims priority to U.S.provisional patent application 60/740,323 filed Nov. 21, 2005, entitled“Devices and Methods for Treating Facet Joints, Uncovertebral Joints,Costovertebral Joints and Other Joints.” U.S. Ser. No. 11/602,713 isalso a continuation-in-part of U.S. Ser. No. 10/997,407, filed Nov. 24,2004 entitled “PATIENT SELECTABLE KNEE JOINT ARTHROPLASTY DEVICES,”which is a continuation-in-part of U.S. Ser. No. 10/752,438, filed Jan.5, 2004 which is a continuation-in-part of U.S. application Ser. No.10/724,010 filed Nov. 25, 2003 entitled “PATIENT SELECTABLE JOINTARTHROPLASTY DEVICES AND SURGICAL TOOLS FACILITATING INCREASED ACCURACY,SPEED AND SIMPLICITY IN PERFORMING TOTAL AND PARTIAL JOINTARTHROPLASTY,” which is a continuation-in-part of U.S. Ser. No.10/305,652 entitled “METHODS AND COMPOSITIONS FOR ARTICULAR REPAIR,”filed Nov. 27, 2002, which is now U.S. Pat. No. 7,468,075, which is acontinuation-in-part of U.S. Ser. No. 10/160,667, filed May 28, 2002,which in turn claims the benefit of U.S. Ser. No. 60/293,488 entitled“METHODS TO IMPROVE CARTILAGE REPAIR SYSTEMS”, filed May 25, 2001, U.S.Ser. No. 60/363,527, entitled “NOVEL DEVICES FOR CARTILAGE REPAIR, filedMar. 12, 2002 and U.S. Ser. Nos. 60/380,695 and 60/380,692, entitled“METHODS AND COMPOSITIONS FOR CARTILAGE REPAIR,” and “METHODS FOR JOINTREPAIR,” filed May 14, 2002, all of which applications are herebyincorporated by reference in their entireties. U.S. Ser. No. 10/997,407is also a continuation-in-part of U.S. application Ser. No. 10/681,750filed Oct. 7, 2003 entitled “MINIMALLY INVASIVE JOINT IMPLANT WITH3-DIMENSIONAL GEOMETRY MATCHING THE ARTICULAR SURFACES and claimsbenefit of U.S. provisional patent application 60/467,686 filed May 2,2003 entitled “JOINT IMPLANTS.” Each of the above-referencedapplications is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to orthopedic methods, systems andprosthetic devices and more particularly relates to methods, systems anddevices associated with treatment of facet joints.

BACKGROUND ART

There are various types of cartilage, e.g., hyaline cartilage andfibrocartilage. Hyaline cartilage is found at the articular surfaces ofbones, e.g., in the joints, and is responsible for providing the smoothgliding motion characteristic of moveable joints. Articular cartilage isfirmly attached to the underlying bones and measures typically less than5 mm in thickness in human joints, with considerable variation dependingon the joint and the site within the joint.

Adult cartilage has a limited ability of repair; thus, damage tocartilage produced by disease, such as rheumatoid and/or osteoarthritis,or trauma can lead to serious physical deformity and debilitation.Furthermore, as human articular cartilage ages, its tensile propertieschange. The superficial zone of the knee articular cartilage exhibits anincrease in tensile strength up to the third decade of life, after whichit decreases markedly with age as detectable damage to type 11 collagenoccurs at the articular surface. The deep zone cartilage also exhibits aprogressive decrease in tensile strength with increasing age, althoughcollagen content does not appear to decrease. These observationsindicate that there are changes in mechanical and, hence, structuralorganization of cartilage with aging that, if sufficiently developed,can predispose cartilage to traumatic damage.

Once damage occurs, joint repair can be addressed through a number ofapproaches. One approach includes the use of matrices, tissue scaffoldsor other carriers implanted with cells (e.g., chondrocytes, chondrocyteprogenitors, stromal cells, mesenchymal stem cells, etc.). Thesesolutions have been described as a potential treatment for cartilage andmeniscal repair or replacement. See, also, International Publications WO99/51719 to Fofonoff, published Oct. 14, 1999; WO01/91672 to Simon etal., published Dec. 6, 2001; and WO01/17463 to Mannsmann, published Mar.15, 2001; U.S. Pat. No. 6,283,980 B1 to Vibe-Hansen et al., issued Sep.4, 2001, U.S. Pat. No. 5,842,477 to Naughton issued Dec. 1, 1998, U.S.Pat. No. 5,769,899 to Schwartz et al. issued Jun. 23, 1998, U.S. Pat.No. 4,609,551 to Caplan et al. issued Sep. 2, 1986, U.S. Pat. No.5,041,138 to Vacanti et al. issued Aug. 29, 1991, U.S. Pat. No.5,197,985 to Caplan et al. issued Mar. 30, 1993, U.S. Pat. No. 5,226,914to Caplan et al. issued Jul. 13, 1993, U.S. Pat. No. 6,328,765 toHardwick et al. issued Dec. 11, 2001, U.S. Pat. No. 6,281,195 to Ruegeret al. issued Aug. 28, 2001, and U.S. Pat. No. 4,846,835 to Grandeissued Jul. 11, 1989. However, clinical outcomes with biologicreplacement materials such as allograft and autograft systems and tissuescaffolds have been uncertain since most of these materials do notachieve a morphologic arrangement or structure similar to or identicalto that of normal, disease-free human tissue it is intended to replace.Moreover, the mechanical durability of these biologic replacementmaterials remains uncertain.

Usually, severe damage or loss of cartilage is treated by replacement ofthe joint with a prosthetic material, for example, silicone, e.g., forcosmetic repairs, or metal alloys. See, e.g., U.S. Pat. No. 6,383,228 toSchmotzer, issued May 7, 2002; U.S. Pat. No. 6,203,576 to Afriat et al.,issued Mar. 20, 2001; U.S. Pat. No. 6,126,690 to Ateshian, et al.,issued Oct. 3, 2000. Implantation of these prosthetic devices is usuallyassociated with loss of underlying tissue and bone without recovery ofthe full function allowed by the original cartilage and, with somedevices, serious long-term complications associated with the loss ofsignificant amount of tissue and bone can include infection, osteolysisand also loosening of the implant.

Further, joint arthroplasties are highly invasive and require surgicalresection of the entire articular surface of one or more bones, or amajority thereof. With these procedures, the marrow space is oftenreamed to fit the stem of the prosthesis. The reaming results in a lossof the patient's bone stock. U.S. Pat. No. 5,593,450 to Scott et al.issued Jan. 14, 1997 discloses an oval domed shaped patella prosthesis.The prosthesis has a femoral component that includes two condyles asarticulating surfaces. The two condyles meet to form a second trochleargroove and ride on a tibial component that articulates with respect tothe femoral component. A patella component is provided to engage thetrochlear groove. U.S. Pat. No. 6,090,144 to Letot et al. issued Jul.18, 2000 discloses a knee prosthesis that includes a tibial componentand a meniscal component that is adapted to be engaged with the tibialcomponent through an asymmetrical engagement.

A variety of materials can be used in replacing a joint with aprosthetic, for example, silicone, e.g. for cosmetic repairs, orsuitable metal alloys are appropriate. See, e.g., U.S. Pat. No.6,443,991 B1 to Running issued Sep. 3, 2002, U.S. Pat. No. 6,387,131 B1to Miehike et al. issued May 14, 2002; U.S. Pat. No. 6,383,228 toSchmotzer issued May 7, 2002; U.S. Pat. No. 6,344,059 B1 to Krakovits etal. issued Feb. 5, 2002; U.S. Pat. No. 6,203,576 to Afriat et al. issuedMar. 20, 2001; U.S. Pat. No. 6,126,690 to Ateshian et al. issued Oct. 3,2000; U.S. Pat. No. 6,013,103 to Kaufman et al. issued Jan. 11, 2000.Implantation of these prosthetic devices is usually associated with lossof underlying tissue and bone without recovery of the full functionallowed by the original cartilage and, with some devices, seriouslong-term complications associated with the loss of significant amountsof tissue and bone can cause loosening of the implant. One suchcomplication is osteolysis. Once the prosthesis becomes loosened fromthe joint, regardless of the cause, the prosthesis will then need to bereplaced. Since the patient's bone stock is limited, the number ofpossible replacement surgeries is also limited for joint arthroplasty.

As can be appreciated, joint arthroplasties are highly invasive andrequire surgical resection of the entire, or a majority of, thearticular surface of one or more bones involved in the repair. Typicallywith these procedures, the marrow space is fairly extensively reamed inorder to fit the stem of the prosthesis within the bone. Reaming resultsin a loss of the patient's bone stock and over time subsequentosteolysis will frequently lead to loosening of the prosthesis. Further,the area where the implant and the bone mate degrades over timerequiring the prosthesis to eventually be replaced. Since the patient'sbone stock is limited, the number of possible replacement surgeries isalso limited for joint arthroplasty. In short, over the course of 15 to20 years, and in some cases even shorter time periods, the patient canrun out of therapeutic options ultimately resulting in a painful,nonfunctional joint.

U.S. Pat. No. 6,206,927 to Fell, et al., issued Mar. 27, 2001, and U.S.Pat. No. 6,558,421 to Fell, et al., issued May 6, 2003, disclose asurgically implantable knee prosthesis that does not require boneresection. This prosthesis is described as substantially elliptical inshape with one or more straight edges. Accordingly, these devices arenot designed to substantially conform to the actual shape (contour) ofthe remaining cartilage in vivo and/or the underlying bone. Thus,integration of the implant can be extremely difficult due to differencesin thickness and curvature between the patient's surrounding cartilageand/or the underlying subchondral bone and the prosthesis. U.S. Pat. No.6,554,866 to Aicher, et al. issued Apr. 29, 2003 describes amono-condylar knee joint prosthesis.

Interpositional knee devices that are not attached to both the tibia andfemur have been described. For example, Platt et al. (1969) “MouldArthroplasty of the Knee,” Journal of Bone and Joint Surgery51B(1):76-87, describes a hemi-arthroplasty with a convex undersurfacethat was not rigidly attached to the tibia. Devices that are attached tothe bone have also been described. Two attachment designs are commonlyused. The McKeever design is a cross-bar member, shaped like a “t” froma top perspective view, that extends from the bone mating surface of thedevice such that the “t” portion penetrates the bone surface while thesurrounding surface from which the “t” extends abuts the bone surface.See McKeever, “Tibial Plateau Prosthesis,” Chapter 7, p. 86. Analternative attachment design is the Macintosh design, which replacesthe “t” shaped fin for a series of multiple flat serrations or teeth.See Potter, “Arthroplasty of the Knee with Tibial Metallic Implants ofthe McKeever and Macintosh Design,” Surg. Clins. Of North Am. 49(4):903-915 (1969).

U.S. Pat. No. 4,502,161 to Wall issued Mar. 5, 1985, describes aprosthetic meniscus constructed from materials such as silicone rubberor Teflon with reinforcing materials of stainless steel or nylonstrands. U.S. Pat. No. 4,085,466 to Goodfellow et al. issued Mar. 25,1978, describes a meniscal component made from plastic materials.Reconstruction of meniscal lesions has also been attempted withcarbon-fiber-polyurethane-poly (L-lactide). Leeslag, et al., Biologicaland Biomechanical Performance of Biomaterials (Christel et al., eds.)Elsevier Science Publishers B.V., Amsterdam. 1986. pp. 347-352.Reconstruction of meniscal lesions is also possible with bioresorbablematerials and tissue scaffolds.

However, currently available devices do not always provide idealalignment with the articular surfaces and the resultant joint congruity.Poor alignment and poor joint congruity can, for example, lead toinstability of the joint.

Thus, there remains a need for compositions for repair of facet joints,uncovertebral joints, and costovertebral joints, among others. Further,there is a need for an implant or implant system that improves theanatomic result of the joint correction procedure by providing surfacesthat more closely resemble the joint anatomy of a patient. Additionally,what is needed is an implant or implant system that provides an improvedfunctional facet, uncovertebral, and costovertebral joint.

SUMMARY

The embodiments described herein provide novel devices and methods forreplacing a portion (e.g., diseased area and/or area slightly largerthan the diseased area) of a facet joint, uncovertebral joint, orcostovertebral joint (e.g., cartilage, and/or bone) with one or moreimplants. In some embodiments, the implant(s) achieve an anatomic ornear anatomic fit with the surrounding structures and tissues.

One embodiment is an interpositional device for use in a facet joint.The device includes a body that is configured to be inserted between thearticular surfaces of the facet joint. The body has first and secondarticular surfaces and first and second ends. The first articularsurface has contours configured to resist motion relative to an opposingarticular surface when the device is inserted between articular surfacesof the facet joint. The second articular surface is configured tofacilitate motion relative to another opposing articular surface whenthe device is inserted between articular surfaces of a facet joint.

Alternate embodiments may include one or more of the following features.The first end can be enlarged relative to a middle portion of thedevice. The first end can form a lip configured to engage at least onesurface of the facet joint and thereby resist motion of the devicerelative to the facet joint. The first end can be configured to belocated in an inter-articular position when the interpositional deviceis implanted in the facet joint, or, alternatively, the first end can beconfigured to be located in an extra-articular position when theinterpositional device is implanted in the facet joint.

The contours of at least a portion of the first articular surfacesubstantially can be made to conform to corresponding contours of theopposing articular surface. At least a portion of the first articularsurface substantially can form a negative of a corresponding portion ofthe opposing articular surface. The first articular surface can beconfigured to secure the device when implanted in the facet joint. Atleast a portion of the first articular surface can be configured tointerdigitate with a corresponding portion of the opposing articularsurface when the device is implanted in the facet joint.

The second articular surface can be substantially smooth.

The second end can be enlarged relative to a middle portion of thedevice such that is enlarges a space between first and second surfacesof the facet joint.

The device can also include an attachment mechanism to secure the devicein a facet join, for example, without limitation, a pin, fin, screw orsuture.

Another embodiment is a patient-specific implant for use in a facetjoint. The implant includes a body configured to be inserted betweenarticular surfaces of the facet joint and that has first and secondarticular surfaces. At least a portion of the first articular surfacesubstantially conforms to a corresponding portion of a first articularsurface of the facet joint. The second articular surface has asubstantially smooth portion configured to engage and move relative to asecond articular surface of the facet joint when the implant is placedbetween the first and second articular surfaces of the facet joint.

Alternate embodiments may include one or more of the following features.The implant may include a first end that is enlarged relative to amiddle portion of the device. The first end may form a cap configured toengage part of the facet joint and thereby resist motion of the devicerelative to the facet joint. The first end can be configured to belocated in an inter-articular position when the interpositional deviceis implanted in the facet joint. The first end can alternatively beconfigured to be located in an extra-articular position when theinterpositional device is implanted in the facet joint.

The first articular surface can be used to secure the device whenimplanted in the facet joint.

The device can further include first and second ends that are enlargedrelative to a middle portion of the device.

The device can also include an attachment mechanism to secure the devicein a facet joint, such as, without limitation, a pin, fin, or screw.

Another embodiment is an interpositional device for use in decompressinga portion of a spine. The device includes a body that can be insertedbetween articular surfaces of a facet joint. The body has first andsecond articular surfaces, a first end portion and a middle portion. Thefirst articular surface is configured to move relative to an opposingarticular surface when the device is in place. The first end portion hasa thickness measured in a direction between the first and secondarticular surfaces that is larger than a corresponding thickness of themiddle portion. The first end portion is configured to resist motion ofthe body relative to the facet joint in at least one direction when theinterpositional device is implanted.

Alternate embodiments may include one or more of the following features.At least a portion of the second articular surface can include contoursthat substantially conform to corresponding contours of a secondarticular surface. At least a portion of the second articular surfacecan substantially form a negative of a corresponding portion of a secondarticular surface. The second articular surface can be configured tosecure the device when implanted in the facet joint. At least a portionof the second articular surface can be configured to interdigitate witha corresponding portion of a second articular surface when the device isimplanted in the facet joint.

The first articular surface can be substantially smooth.

Another embodiment is a device for use in relieving pressure on aportion of a spine. The device has a body configured to be insertedbetween articular surfaces of a facet joint. The body has first andsecond articular surfaces and an end portion. The first articularsurface is configured to engage a corresponding first surface of thefacet joint when the device is implanted. The second articular surfaceis configured to engage a corresponding second surface of the facetjoint when the device is implanted. The end portion is relativelythicker in a direction between the first and second surfaces than anadjacent portion of the device, and thereby increases the spacingbetween the first and second surfaces of the facet joint when the deviceis implanted in the facet joint.

Another embodiment is a method for decompressing a portion of a spine.The method includes inserting an implant between first and secondarticular surfaces of a facet joint to expand a space between thearticular surfaces; and stabilizing the implant in the facet joint suchthat the first and second surfaces remain in an expanded position for aperiod of time. As a result, the portion of the spine decompresses.

Alternate embodiments may include one or more of the following features.The pressure on an adjacent interstitial space of the spine can bereduced. Pain associated with pressure on the spine can be subsequentlyreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIG. 1A is a block diagram of a method for assessing a joint in needof repair according to embodiments of the invention wherein the existingjoint surface is unaltered, or substantially unaltered, prior toreceiving the selected implant.

FIG. 1B is a block diagram of a method for assessing a joint in need ofrepair according to embodiments of the invention wherein the existingjoint surface is unaltered, or substantially unaltered, prior todesigning an implant suitable to achieve the repair.

FIG. 1C is a block diagram of a method for developing an implant andusing the implant in a patient.

FIG. 2A is a perspective view of a joint implant of embodiments of theinvention suitable for implantation in a joint.

FIG. 2B is a top view of the implant of FIG. 2A.

FIG. 2C is a cross-sectional view of the implant of FIG. 2A along thelines 2C-2C shown in FIG. 2B.

FIG. 2D is a cross-sectional view along the lines 2D-2D shown in FIG.2B.

FIG. 2E is a cross-sectional view along the lines 2E-2E shown in FIG.2B.

FIG. 2F is a side view of the implant of FIG. 2A.

FIG. 2G is a cross-sectional view of the implant of FIG. 2A shownimplanted taken along a plane parallel to the sagittal plane.

FIG. 2H is a cross-sectional view of the implant of FIG. 2A shownimplanted taken along a plane parallel to the coronal plane.

FIG. 2I is a cross-sectional view of the implant of FIG. 2A shownimplanted taken along a plane parallel to the axial plane.

FIG. 2J shows a slightly larger implant that extends closer to the bonemedially (towards the edge of the tibial plateau) and anteriorly andposteriorly.

FIG. 2K is a side view of an alternate embodiment of the joint implantof FIG. 2A showing an anchor in the form of a keel.

FIG. 2L is a bottom view of an alternate embodiment of the joint implantof FIG. 2A showing an anchor.

FIG. 2M shows an anchor in the form of a cross-member.

FIGS. 2N1-O1 and 2N2-O2 are alternative embodiments of the implantshowing the lower surface have a trough for receiving a cross-bar.

FIG. 2P illustrates a variety of cross-bars.

FIGS. 2Q-R illustrate the device implanted within a joint.

FIGS. 2S(1-9) illustrate another implant suitable for the tibial plateaufurther having a chamfer cut along one edge.

FIG. 2T(1-8) illustrate an alternate embodiment of the tibial implantwherein the surface of the joint is altered to create a flat or angledsurface for the implant to mate with.

FIG. 3A is an example of a cross-section of a vertebra demonstrating onenormal and one degenerated facet joint.

FIG. 3B is an expanded view of the degenerated facet joint shown in FIG.3A.

FIG. 4 is an example of a surgical instrument for removal of boneovergrowth and spurs.

FIGS. 5A-C are examples of various embodiments of a surgical instrumentfor shaping and smoothing the articular surface.

FIGS. 6A-D are examples of various embodiments of an instrument forshaping a facet or other joint and for inserting an implant. Theinstrument may have a round 601A or tapered tip 601B.

FIG. 7 is an example of an instrument with a shaver 700.

FIGS. 8A-C are examples of various embodiments of a distraction devicefor preparing a joint for implant insertion.

FIGS. 9A-D show various embodiments for distracting the joint andfacilitating implant insertion.

FIGS. 10A-F show various embodiments describing various types of implantmargin, including tapered designs 1001 and round designs 1002.

FIG. 11 shows a facet device for implantation into a facet joint, inaccordance with one embodiment of the invention.

FIG. 12 shows a facet device having a dumbbell shape, in accordance withone embodiment of the invention.

FIG. 13 shows a facet device having a dumbbell shape, in accordance withone embodiment of the invention.

FIG. 14 shows a bone spur on a surface associated with a facet joint.

FIG. 15 shows a facet device capable of changing position or orientationof one or two facet joints, optionally by moving bone spurs or bonyexcrescences, thereby reducing spinal stenosis, in accordance with oneembodiment of the invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use embodiments of the invention. Variousmodifications to the embodiments described will be readily apparent tothose skilled in the art, and the generic principles defined herein canbe applied to other embodiments and applications without departing fromthe spirit and scope of the present invention as defined by the appendedclaims. Thus, embodiments of the present invention are not intended tobe limited to the embodiments shown, but are to be accorded the widestscope consistent with the principles and features disclosed herein. Tothe extent necessary to achieve a complete understanding of theinvention disclosed, the specification and drawings of all issuedpatents, patent publications, and patent applications cited in thisapplication are incorporated herein by reference in their entirety.

As will be appreciated by those of skill in the art, methods recitedherein may be carried out in any order of the recited events which islogically possible, as well as the recited order of events. Furthermore,where a range of values is provided, it is understood that everyintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within embodiments of the invention. Also, it iscontemplated that any optional feature of the inventive variationsdescribed may be set forth and claimed independently, or in combinationwith any one or more of the features described herein.

The practice of embodiments of the present invention can employ, unlessotherwise indicated, conventional and digital methods of x-ray imagingand processing, x-ray tomosynthesis, ultrasound including A-scan, B-scanand C-scan, computed tomography (CT scan), magnetic resonance imaging(MRI), optical coherence tomography, single photon emission tomography(SPECT) and positron emission tomography (PET) within the skill of theart. Such techniques are explained fully in the literature and need notbe described herein. See, e.g., X-Ray Structure Determination: APractical Guide, 2nd Edition, editors Stout and Jensen, 1989, John Wiley& Sons, publisher; Body CT: A Practical Approach, editor Slone, 1999,McGraw-Hill publisher; X-ray Diagnosis: A Physician's Approach, editorLam, 1998 Springer-Verlag, publisher; and Dental Radiology:Understanding the X-Ray Image, editor Laetitia Brocklebank 1997, OxfordUniversity Press publisher. See also, The Essential Physics of MedicalImaging (2.sup.nd Ed.), Jerrold T. Bushberg, et al.

The present invention provides methods and compositions for repairingjoints, particularly for repairing articular cartilage and subchondralbone and for facilitating the integration of a wide variety of cartilageand subchondral bone repair materials into a subject. Among otherthings, the techniques described herein allow for the customization ofcartilage or subchondral bone repair material to suit a particularsubject, for example in terms of size, cartilage thickness and/orcurvature including subchondral bone curvature. When the shape (e.g.,size, thickness and/or curvature) of the articular cartilage surface isan exact or near anatomic fit with the non-damaged cartilage or with thesubject's original cartilage, the success of repair is enhanced. Therepair material can be shaped prior to implantation and such shaping canbe based, for example, on electronic images that provide informationregarding curvature or thickness of any “normal” cartilage surroundingthe defect and/or on curvature of the bone underlying the defect. Thus,embodiments of the invention provide, among other things, for minimallyinvasive methods for partial or complete joint replacement with attachedand interpositional designs. The methods require only minimal or, insome instances, no loss in bone stock. Additionally, unlike with currenttechniques, the methods described herein will help to restore theintegrity of the articular surface by achieving an exact or nearanatomic match between the implant and the surrounding or adjacentcartilage and/or subchondral bone.

Advantages of embodiments of the present invention can include, but arenot limited to, (i) optional customization of joint repair, therebyenhancing the efficacy and comfort level for the patient following therepair procedure; (ii) optional eliminating the need for a surgeon tomeasure the defect to be repaired intraoperatively in some embodiments;(iii) optional eliminating the need for a surgeon to shape the materialduring the implantation procedure; (iv) providing methods of evaluatingcurvature of the repair material based on bone or tissue images or basedon intraoperative probing techniques; (v) providing methods of repairingjoints with only minimal or, in some instances, no loss in bone stock;(vi) improving postoperative joint congruity; (vii) improving thepostoperative patient recovery in some embodiments and (viii) improvingpostoperative function, such as range of motion.

Thus, the methods described herein allow for the design and use of jointrepair material that more precisely fits the defect (e.g. site ofimplantation) or the articular surface(s) and, accordingly, providesimproved repair of the joint.

Assessment of Joints and Alignment

The methods and compositions described herein can be used to treatdefects resulting from disease of the cartilage (e.g., osteoarthritis),bone damage, cartilage damage, trauma, and/or degeneration due tooveruse or age. Embodiments of the invention allow, among other things,a health practitioner to evaluate and treat such defects. The size,volume and shape of the area of interest can include only the region ofcartilage that has the defect, but preferably will also includecontiguous parts of the cartilage surrounding the cartilage defect.

As will be appreciated by those of skill in the art, size, curvatureand/or thickness measurements can be obtained using any suitabletechnique. For example, one-dimensional, two-dimensional, and/orthree-dimensional measurements can be obtained using suitable mechanicalmeans, laser devices, electromagnetic or optical tracking systems,molds, materials applied to the articular surface that harden and“memorize the surface contour,” and/or one or more imaging techniquesknown in the art. Measurements can be obtained non-invasively and/orintraoperatively (e.g., using a probe or other surgical device). As willbe appreciated by those of skill in the art, the thickness of the repairdevice can vary at any given point depending upon patient's anatomyand/or the depth of the damage to the cartilage and/or bone to becorrected at any particular location on an articular surface.

FIG. 1A is a flow chart showing steps taken by a practitioner inassessing a joint. First, a practitioner obtains a measurement of atarget joint 10. The step of obtaining a measurement can be accomplishedby taking an image of the joint. This step can be repeated, asnecessary, 11 to obtain a plurality of images in order to further refinethe joint assessment process. Once the practitioner has obtained thenecessary measurements, the information is used to generate a modelrepresentation of the target joint being assessed 30. This modelrepresentation can be in the form of a topographical map or image. Themodel representation of the joint can be in one, two, or threedimensions. It can include a physical model. More than one model can becreated 31, if desired. Either the original model, or a subsequentlycreated model, or both can be used. After the model representation ofthe joint is generated 30, the practitioner can optionally generate aprojected model representation of the target joint in a correctedcondition 40, e.g., from the existing cartilage on the joint surface, byproviding a mirror of the opposing joint surface, or a combinationthereof. Again, this step can be repeated 41, as necessary or desired.Using the difference between the topographical condition of the jointand the projected image of the joint, the practitioner can then select ajoint implant 50 that is suitable to achieve the corrected jointanatomy. As will be appreciated by those of skill in the art, theselection process 50 can be repeated 51 as often as desired to achievethe desired result. Additionally, it is contemplated that a practitionercan obtain a measurement of a target joint 10 by obtaining, for example,an x-ray, and then select a suitable joint replacement implant 50.

As will be appreciated by those of skill in the art, the practitionercan proceed directly from the step of generating a model representationof the target joint 30 to the step of selecting a suitable jointreplacement implant 50 as shown by the arrow 32. Additionally, followingselection of suitable joint replacement implant 50, the steps ofobtaining measurement of target joint 10, generating modelrepresentation of target joint 30 and generating projected model 40, canbe repeated in series or parallel as shown by the flow 24, 25, 26.

FIG. 1B is an alternate flow chart showing steps taken by a practitionerin assessing a joint. First, a practitioner obtains a measurement of atarget joint 10. The step of obtaining a measurement can be accomplishedby taking an image of the joint. This step can be repeated, asnecessary, 11 to obtain a plurality of images in order to further refinethe joint assessment process. Once the practitioner has obtained thenecessary measurements, the information is used to generate a modelrepresentation of the target joint being assessed 30. This modelrepresentation can be in the form of a topographical map or image. Themodel representation of the joint can be in one, two, or threedimensions. The process can be repeated 31 as necessary or desired. Itcan include a physical model. After the model representation of thejoint is assessed 30, the practitioner can optionally generate aprojected model representation of the target joint in a correctedcondition 40. This step can be repeated 41 as necessary or desired.Using the difference between the topographical condition of the jointand the projected image of the joint, the practitioner can then design ajoint implant 52 that is suitable to achieve the corrected jointanatomy, repeating the design process 53 as often as necessary toachieve the desired implant design. The practitioner can also assesswhether providing additional features, such as rails, keels, lips, pegs,cruciate stems, or anchors, cross-bars, etc. will enhance the implants'performance in the target joint.

As will be appreciated by those of skill in the art, the practitionercan proceed directly from the step of generating a model representationof the target joint 30 to the step of designing a suitable jointreplacement implant 52 as shown by the arrow 38. Similar to the flowshown above, following the design of a suitable joint replacementimplant 52, the steps of obtaining measurement of target joint 10,generating model representation of target joint 30 and generatingprojected model 40, can be repeated in series or parallel as shown bythe flow 42, 43, 44.

FIG. 1C is a flow chart illustrating the process of selecting an implantfor a patient. First, using the techniques described above or thosesuitable and known in the art at the time embodiments of the inventionare practiced, the size of area of diseased cartilage or cartilage lossis measured 100. This step can be repeated multiple times 101, asdesired. Once the size of the cartilage defect is measured, thethickness of adjacent cartilage can optionally be measured 110. Thisprocess can also be repeated as desired 111. Either after measuring thecartilage loss or measuring the thickness of adjacent cartilage, thecurvature of the articular surface is then measured 120. Alternatively,the subchondral bone can be measured. As will be appreciatedmeasurements can be taken of the surface of the joint being repaired, orof the mating surface in order to facilitate development of the bestdesign for the implant surface.

Once the surfaces have been measured, the user either selects the bestfitting implant contained in a library of implants 130 or generates apatient-specific implant 132. These steps can be repeated as desired ornecessary to achieve the best fitting implant for a patient, 131, 133.As will be appreciated by those of skill in the art, the process ofselecting or designing an implant can be tested against the informationcontained in the MRI or x-ray of the patient to ensure that the surfacesof the device achieves a good fit relative to the patient's jointsurface. Testing can be accomplished by, for example, superimposing theimplant image over the image for the patient's joint. Once it has beendetermined that a suitable implant has been selected or designed, theimplant site can be prepared 140, for example by removing cartilage orbone from the joint surface, or the implant can be placed into the joint150.

The joint implant selected or designed achieves anatomic or nearanatomic fit with the existing surface of the joint while presenting amating surface for the opposing joint surface that replicates thenatural joint anatomy. In this instance, both the existing surface ofthe joint can be assessed as well as the desired resulting surface ofthe joint. This technique is particularly useful for implants that arenot anchored into the bone.

As will be appreciated by those of skill in the art, the physician, orother person practicing embodiments of the invention, can obtain ameasurement of a target joint 10 and then either design 52 or select 50a suitable joint replacement implant.

Repair Materials

A wide variety of materials find use in the practice of the presentinvention, including, but not limited to, plastics, metals, crystal freemetals, ceramics, biological materials (e.g., collagen or otherextracellular matrix materials), hydroxyapatite, cells (e.g., stemcells, chondrocyte cells or the like), or combinations thereof. Based onthe information (e.g., measurements) obtained regarding the defect andthe articular surface and/or the subchondral bone, a repair material canbe formed or selected. Further, using one or more of these techniquesdescribed herein, a cartilage or bone replacement or regeneratingmaterial having a curvature that will fit into a particular cartilagedefect or onto a particular bone surface, will follow the contour andshape of the articular surface, and will optionally match the thicknessof the surrounding cartilage. The repair material can include anycombination of materials, and typically includes at least onenon-pliable material, for example materials that are not easily bent orchanged.

A. Metal and Polymeric Repair Materials

Currently, joint repair systems often employ metal and/or polymericmaterials including, for example, prostheses which are anchored into theunderlying bone (e.g., a femur in the case of a knee prosthesis). See,e.g., U.S. Pat. No. 6,203,576 to Afriat, et al. issued Mar. 20, 2001 andU.S. Pat. No. 6,322,588 to Ogle, et al. issued Nov. 27, 2001, andreferences cited therein. A wide-variety of metals are useful in thepractice of embodiments of the present invention, and can be selectedbased on any criteria. For example, material selection can be based onresiliency to impart a desired degree of rigidity. Non-limiting examplesof suitable metals include silver, gold, platinum, palladium, iridium,copper, tin, lead, antimony, bismuth, zinc, titanium, cobalt, stainlesssteel, nickel, iron alloys, cobalt alloys, such as Elgiloy®), acobalt-chromium-nickel alloy, and MP35N, anickel-cobalt-chromium-molybdenum alloy, and Nitinol®, a nickel-titaniumalloy, aluminum, manganese, iron, tantalum, crystal free metals, such asLiquidmetal® alloys (available from LiquidMetal Technologies,www.liquidmetal.com), other metals that can slowly form polyvalent metalions, for example to inhibit calcification of implanted substrates incontact with a patient's bodily fluids or tissues, and combinationsthereof.

Suitable synthetic polymers include, without limitation, polyamides(e.g., nylon), polyesters, polystyrenes, polyacrylates, vinyl polymers(e.g., polyethylene, polytetrafluoroethylene, polypropylene andpolyvinyl chloride), polycarbonates, polyurethanes, poly dimethylsiloxanes, cellulose acetates, polymethyl methacrylates, polyether etherketones, ethylene vinyl acetates, polysulfones, nitrocelluloses, similarcopolymers and mixtures thereof. Bioresorbable synthetic polymers canalso be used such as dextran, hydroxyethyl starch, derivatives ofgelatin, polyvinylpyrrolidone, polyvinyl alcohol,poly[N-(2-hydroxypropyl) methacrylamide], poly(hydroxy acids),poly(epsilon-caprolactone), polylactic acid, polyglycolic acid,poly(dimethyl glycolic acid), poly(hydroxy butyrate), and similarcopolymers can also be used.

Other materials would also be appropriate, for example, the polyketoneknown as polyetheretherketone (PEEK®). This includes the material PEEK450G, which is an unfilled PEEK approved for medical implantationavailable from Victrex of Lancashire, Great Britain. (Victrex is locatedat www.matweb.com or see Boedeker www.boedeker.com). Other sources ofthis material include Gharda located in Panoli, India(www.ghardapolymers.com).

It should be noted that the material selected can also be filled. Forexample, other grades of PEEK are also available and contemplated, suchas 30% glass-filled or 30% carbon filled, provided such materials arecleared for use in implantable devices by the FDA, or other regulatorybody. Glass filled PEEK reduces the expansion rate and increases theflexural modulus of PEEK relative to that portion which is unfilled. Theresulting product is known to be ideal for improved strength, stiffness,or stability. Carbon filled PEEK is known to enhance the compressivestrength and stiffness of PEEK and lower its expansion rate. Carbonfilled PEEK offers wear resistance and load carrying capability.

As will be appreciated, other suitable similarly biocompatiblethermoplastic or thermoplastic polycondensate materials that resistfatigue, have good memory, are flexible, and/or deflectable have verylow moisture absorption, and good wear and/or abrasion resistance, canbe used without departing from the scope of embodiments of theinvention. The implant can also be comprised of polyetherketoneketone(PEKK).

Other materials that can be used include polyetherketone (PEK),polyetherketoneetherketoneketone (PEKEKK), andpolyetheretherketoneketone (PEEKK), and generally apolyaryletheretherketone. Further other polyketones can be used as wellas other thermoplastics.

Reference to appropriate polymers that can be used for the implant canbe made to the following documents, all of which are incorporated hereinby reference. These documents include: PCT Publication WO 02/02158 A1,dated Jan. 10, 2002 and entitled Bio-Compatible Polymeric Materials; PCTPublication WO 02/00275 A1, dated Jan. 3, 2002 and entitledBio-Compatible Polymeric Materials; and PCT Publication WO 02/00270 A1,dated Jan. 3, 2002 and entitled Bio-Compatible Polymeric Materials.

The polymers can be prepared by any of a variety of approaches includingconventional polymer processing methods. Preferred approaches include,for example, injection molding, which is suitable for the production ofpolymer components with significant structural features, and rapidprototyping approaches, such as reaction injection molding andstereo-lithography. The substrate can be textured or made porous byeither physical abrasion or chemical alteration to facilitateincorporation of the metal coating. Other processes are alsoappropriate, such as extrusion, injection, compression molding and/ormachining techniques. Typically, the polymer is chosen for its physicaland mechanical properties and is suitable for carrying and spreading thephysical load between the joint surfaces.

More than one metal and/or polymer can be used in combination with eachother. For example, one or more metal-containing substrates can becoated with polymers in one or more regions or, alternatively, one ormore polymer-containing substrate can be coated in one or more regionswith one or more metals.

The system or prosthesis can be porous or porous coated. The poroussurface components can be made of various materials including metals,ceramics, and polymers. These surface components can, in turn, besecured by various means to a multitude of structural cores formed ofvarious metals. Suitable porous coatings include, but are not limitedto, metal, ceramic, polymeric (e.g., biologically neutral elastomerssuch as silicone rubber, polyethylene terephthalate and/or combinationsthereof or combinations thereof. See, e.g., U.S. Pat. No. 3,605,123 toHahn, issued Sep. 20, 1971. U.S. Pat. No. 3,808,606 to Tronzo issued May7, 1974 and U.S. Pat. No. 3,843,975 to Tronzo issued Oct. 29, 1974; U.S.Pat. No. 3,314,420 to Smith issued Apr. 18, 1967; U.S. Pat. No.3,987,499 to Scharbach issued Oct. 26, 1976; and GermanOffenlegungsschrift U.S. Pat. No. 2,306,552. There can be more than onecoating layer and the layers can have the same or different porosities.See, e.g., U.S. Pat. No. 3,938,198 to Kahn, et al., issued Feb. 17,1976.

The coating can be applied by surrounding a core with powdered polymerand heating until cured to form a coating with an internal network ofinterconnected pores. The tortuosity of the pores (e.g., a measure oflength to diameter of the paths through the pores) can be important inevaluating the probable success of such a coating in use on a prostheticdevice. See, also, U.S. Pat. No. 4,213,816 to Morris issued Jul. 22,1980. The porous coating can be applied in the form of a powder and thearticle as a whole subjected to an elevated temperature that bonds thepowder to the substrate. Selection of suitable polymers and/or powdercoatings can be determined in view of the teachings and references citedherein, for example based on the melt index of each.

B. Biological Repair Material

Repair materials can also include one or more biological material eitheralone or in combination with non-biological materials. For example, anybase material can be designed or shaped and suitable cartilagereplacement or regenerating material(s) such as fetal cartilage cellscan be applied to be the base. The cells can be then be grown inconjunction with the base until the thickness (and/or curvature) of thecartilage surrounding the cartilage defect has been reached. Conditionsfor growing cells (e.g., chondrocytes) on various substrates in culture,ex vivo and in vivo are described, for example, in U.S. Pat. No.5,478,739 to Slivka et al. issued Dec. 26, 1995; U.S. Pat. No. 5,842,477to Naughton et al. issued Dec. 1, 1998; U.S. Pat. No. 6,283,980 toVibe-Hansen et al., issued Sep. 4, 2001, and U.S. Pat. No. 6,365,405 toSalzmann et al. issued Apr. 2, 2002. Non-limiting examples of suitablesubstrates include plastic, tissue scaffold, a bone replacement material(e.g., a hydroxyapatite, a bioresorbable material), or any othermaterial suitable for growing a cartilage replacement or regeneratingmaterial on it.

Biological polymers can be naturally occurring or produced in vitro byfermentation and the like. Suitable biological polymers include, withoutlimitation, collagen, elastin, silk, keratin, gelatin, polyamino acids,cat gut sutures, polysaccharides (e.g., cellulose and starch) andmixtures thereof. Biological polymers can be bioresorbable.

Biological materials used in the methods described herein can beautografts (from the same subject); allografts (from another individualof the same species) and/or xenografts (from another species). See,also, International Patent Publications WO 02/22014 to Alexander et al.published Mar. 21, 2002 and WO 97/27885 to Lee published Aug. 7, 1997.In certain embodiments autologous materials are preferred, as they cancarry a reduced risk of immunological complications to the host,including re-absorption of the materials, inflammation and/or scarringof the tissues surrounding the implant site.

In one embodiment of the invention, a probe is used to harvest tissuefrom a donor site and to prepare a recipient site. The donor site can belocated in a xenograft, an allograft or an autograft. The probe is usedto achieve a good anatomic match between the donor tissue sample and therecipient site. The probe is specifically designed to achieve a seamlessor near seamless match between the donor tissue sample and the recipientsite. The probe can, for example, be cylindrical. The distal end of theprobe is typically sharp in order to facilitate tissue penetration.Additionally, the distal end of the probe is typically hollow in orderto accept the tissue. The probe can have an edge at a defined distancefrom its distal end, e.g., at 1 cm distance from the distal end and theedge can be used to achieve a defined depth of tissue penetration forharvesting. The edge can be external or can be inside the hollow portionof the probe. For example, an orthopedic surgeon can take the probe andadvance it with physical pressure into the cartilage, the subchondralbone and the underlying marrow in the case of a joint such as a kneejoint. The surgeon can advance the probe until the external or internaledge reaches the cartilage surface. At that point, the edge will preventfurther tissue penetration thereby achieving a constant and reproducibletissue penetration. The distal end of the probe can include one or moreblades, saw-like structures, or tissue cutting mechanism. For example,the distal end of the probe can include an iris-like mechanismconsisting of several small blades. The blade or blades can be movedusing a manual, motorized or electrical mechanism thereby cuttingthrough the tissue and separating the tissue sample from the underlyingtissue. Typically, this will be repeated in the donor and the recipient.In the case of an iris-shaped blade mechanism, the individual blades canbe moved so as to close the iris thereby separating the tissue samplefrom the donor site.

In another embodiment of the invention, a laser device or aradiofrequency device can be integrated inside the distal end of theprobe. The laser device or the radiofrequency device can be used to cutthrough the tissue and to separate the tissue sample from the underlyingtissue.

In one embodiment of the invention, the same probe can be used in thedonor and in the recipient. In another embodiment, similarly shapedprobes of slightly different physical dimensions can be used. Forexample, the probe used in the recipient can be slightly smaller thanthat used in the donor thereby achieving a tight fit between the tissuesample or tissue transplant and the recipient site. The probe used inthe recipient can also be slightly shorter than that used in the donorthereby correcting for any tissue lost during the separation or cuttingof the tissue sample from the underlying tissue in the donor material.

Any biological repair material can be sterilized to inactivatebiological contaminants such as bacteria, viruses, yeasts, molds,mycoplasmas and parasites. Sterilization can be performed using anysuitable technique, for example radiation, such as gamma radiation.

Any of the biological materials described herein can be harvested withuse of a robotic device. The robotic device can use information from anelectronic image for tissue harvesting.

In certain embodiments, the cartilage replacement material has aparticular biochemical composition. For instance, the biochemicalcomposition of the cartilage surrounding a defect can be assessed bytaking tissue samples and chemical analysis or by imaging techniques.For example, WO 02/22014 to Alexander describes the use of gadoliniumfor imaging of articular cartilage to monitor glycosaminoglycan contentwithin the cartilage. The cartilage replacement or regenerating materialcan then be made or cultured in a manner, to achieve a biochemicalcomposition similar to that of the cartilage surrounding theimplantation site. The culture conditions used to achieve the desiredbiochemical compositions can include, for example, varyingconcentrations. Biochemical composition of the cartilage replacement orregenerating material can, for example, be influenced by controllingconcentrations and exposure times of certain nutrients and growthfactors.

Device Design A. Cartilage and Bone Models

Using information on thickness and curvature of the cartilage orunderlying bone, a physical model of the surfaces of the articularcartilage and of the underlying bone can be created. This physical modelcan be representative of a limited area within the joint or it canencompass the entire joint. This model can also take into considerationthe presence or absence of a meniscus as well as the presence or absenceof some or all of the cartilage. For example, in the knee joint, thephysical model can encompass only the medial or lateral femoral condyle,both femoral condyles and the notch region, the medial tibial plateau,the lateral tibial plateau, the entire tibial plateau, the medialpatella, the lateral patella, the entire patella or the entire joint.The location of a diseased area of cartilage can be determined, forexample using a 3D coordinate system or a 3D Euclidian distance asdescribed in WO 02/22014.

In this way, the size of the defect to be repaired can be determined.This process takes into account that, for example, roughly 80% ofpatients have a healthy lateral component. As will be apparent, some,but not all, defects will include less than the entire cartilage. Thus,in one embodiment of the invention, the thickness of the normal or onlymildly diseased cartilage surrounding one or more cartilage defects ismeasured. This thickness measurement can be obtained at a single pointor, preferably, at multiple points, for example 2 point, 4-6 points,7-10 points, more than 10 points or over the length of the entireremaining cartilage. Furthermore, once the size of the defect isdetermined, an appropriate therapy (e.g., articular repair system) canbe selected such that as much as possible of the healthy, surroundingtissue is preserved.

In other embodiments, the curvature of the articular surface orsubchondral bone can be measured to design and/or shape the repairmaterial. Further, both the thickness of the remaining cartilage and thecurvature of the articular surface including bone can be measured todesign and/or shape the repair material. Alternatively, the curvature ofthe subchondral bone can be measured and the resultant measurement(s)can be used to either select or shape a cartilage replacement material.For example, the contour of the subchondral bone can be used tore-create a virtual cartilage surface: the margins of an area ofdiseased cartilage can be identified. The subchondral bone shape in thediseased areas can be measured. A virtual contour can then be created bycopying the subchondral bone surface into the cartilage surface, wherebythe copy of the subchondral bone surface connects the margins of thearea of diseased cartilage. In shaping the device, the contours can beconfigured to mate with existing cartilage or to account for the removalof some or all of the cartilage.

FIG. 2A shows a slightly perspective top view of a joint implant 200 ofone embodiment of the invention suitable for implantation in a jointsuch as a facet joint, an uncovertebral joint of a costovertebral joint.As shown in FIG. 2A, the implant can be generated using, for example, adual surface assessment, as described above with respect to FIGS. 1A andB.

The implant 200 has an upper or frontal surface 202, a lower orposterior surface 204 and, optionally, a peripheral edge 206. The upperor frontal surface 202 is formed so that it forms a mating surface forreceiving the opposing joint surface; in this instance partially concaveto receive a femur, although other joints such as a facet joint, anuncovertebral joint or a costovertebral joint are possible. The concavesurface can be variably concave such that it presents a surface to theopposing joint surface, e.g. a negative surface of the mating surface ofthe femur it communicates with. As will be appreciated by those of skillin the art, the negative impression need not be a perfect one.

The upper or frontal surface 202 of the implant 200 can be shaped by anyof a variety of means. For example, the upper or frontal surface 202 canbe shaped by projecting the surface from the existing cartilage and/orbone surfaces on the articular surface such as a tibial plateau or thesurface of a facet joint, or it can be shaped to mirror the femoralcondyle in order to optimize the complimentary surface of the implantwhen it engages the femoral condyle. Alternatively, the superior surface202 can be configured to mate with an inferior surface of an implantconfigured for the opposing femoral condyle.

The lower or posterior surface 204 has optionally a convex surface thatmatches, or nearly matches, the surface of the joint, e.g. a tibialplateau or a facet or uncovertebral or costovertebral joint, such thatit creates an anatomic or near anatomic fit with the tibial plateau orother relevant or applicable articular surface. Depending on the shapeof the tibial plateau or applicable articular surface, the lower orposterior surface can be partially convex as well. Thus, the lower orposterior surface 204 presents a surface to the tibial plateau orapplicable articular surface that fits within the existing surface. Itcan be formed to match the existing surface or to match the surfaceafter articular resurfacing.

As will be appreciated by those of skill in the art, the convex surfaceof the lower or posterior surface 204 need not be perfectly convex.Rather, the lower or posterior surface 204 is more likely consist ofconvex and concave portions that fit within the existing surface of thetibial plateau or the re-surfaced plateau or re-surfaced applicablearticular surface. Thus, the surface is essentially variably convex andconcave.

FIG. 2B shows a top view of the joint implant of FIG. 2A. As shown inFIG. 2B the exterior shape 208 of the implant can be elongated. Theelongated form can take a variety of shapes including elliptical,quasi-elliptical, race-track, etc. However, as will be appreciated theexterior dimension can be irregular thus not forming a true geometricshape, e.g., ellipse. As will be appreciated by those of skill in theart, the actual exterior shape of an implant can vary depending on thenature of the joint defect to be corrected. Thus, the ratio of thelength L to the width W can vary from, for example, between about 0.25to about 2.0, and more specifically from about 0.5 to about 1.5. Asfurther shown in FIG. 2B, the length across an axis of the implant 200varies when taken at points along the width of the implant. For example,as shown in FIG. 2B, L.sub.1.noteq.L.sub.2.noteq.L.sub.3.

Turning now to FIGS. 2C-E, cross-sections of the implant shown in FIG.2B are depicted along the lines of 2C-2C, 2D-2D, and 2E-2E. The implanthas a thickness t1, t2 and t3 respectively. As illustrated by thecross-sections, the thickness of the implant varies along both itslength L and width W. The actual thickness at a particular location ofthe implant 200 is a function of the thickness of the cartilage and/orbone to be replaced and the joint mating surface to be replicated.Further, the profile of the implant 200 at any location along its lengthL or width W is a function of the cartilage and/or bone to be replaced.

FIG. 2F is a lateral view of the implant 200 of FIG. 2A. In thisinstance, the height of the implant 200 at a first end h.sub.1 isdifferent than the height of the implant at a second end h.sub.2.Further the upper edge 208 can have an overall slope in a downwarddirection. However, as illustrated the actual slope of the upper edge208 varies along its length and can, in some instances, be a positiveslope. Further the lower edge 210 can have an overall slope in adownward direction. As illustrated the actual slope of the lower edge210 varies along its length and can, in some instances, be a positiveslope. As will be appreciated by those of skill in the art, depending onthe anatomy of an individual patient, an implant can be created whereinh.sub.1 and h.sub.2 are equivalent, or substantially equivalent withoutdeparting from the scope of the invention.

FIG. 2G is a cross-section taken along a sagittal plane in a bodyshowing the implant 200 implanted within a knee joint 1020 such that thelower surface 204 of the implant 200 lies on the tibial plateau 1022 andthe femur 1024 rests on the upper surface 202 of the implant 200. FIG.2H is a cross-section taken along a coronal plane in a body showing theimplant 200 implanted within a knee joint 1020. As is apparent from thisview, the implant 200 is positioned so that it fits within a superiorarticular surface 224. As will be appreciated by those of skill in theart, the articular surface could be the medial or lateral facet, asneeded.

FIG. 2I is a view along an axial plane of the body showing the implant200 implanted within a knee joint 1020 showing the view taken from anaerial, or upper, view. FIG. 2J is a view of an alternate embodimentwhere the implant is a bit larger such that it extends closer to thebone medially, i.e., towards the edge 1023 of the tibial plateau, aswell as extending anteriorly and posteriorly.

FIG. 2K is a cross-section of an implant 200 of one embodiment of theinvention, e.g., for a facet joint, an uncovertebral or a costovertebraljoint, according to an alternate embodiment. In this embodiment, thelower surface 204 further includes a joint anchor 212. As illustrated inthis embodiment, the joint anchor 212 forms a protrusion, keel orvertical member that extends from the lower surface 204 of the implant200 and projects into, for example, the bone of the joint. As will beappreciated by those of skill in the art, the keel can be perpendicularor lie within a plane of the body.

Additionally, as shown in FIG. 2L, the joint anchor 212 can have across-member 214 so that from a bottom perspective, the joint anchor 212has the appearance of a cross or an “x.” As will be appreciated by thoseof skill in the art, the joint anchor 212 could take on a variety ofother forms while still accomplishing the same objective of providingincreased stability of the implant 200 in the joint. These formsinclude, but are not limited to, pins, bulbs, balls, teeth, etc.Additionally, one or more joint anchors 212 can be provided as desired.FIGS. 2M and N illustrate cross-sections of alternate embodiments of adual component implant from a side view and a front view.

In an alternate embodiment shown in FIG. 2M, it may be desirable toprovide one or more cross-members 220 on the lower surface 204 in orderto provide a bit of translation movement of the implant relative to thesurface of the femur or applicable articular surface, or femur implant.In that event, the cross-member can be formed integral to the surface ofthe implant or can be one or more separate pieces that fit within agroove 222 on the lower surface 204 of the implant 200. The groove canform a single channel as shown in FIG. 2N1, or can have more than onechannel as shown in FIG. 2O1. In either event, the cross-bar then fitswithin the channel as shown in FIGS. 2N2-O2. The cross-bar members 220can form a solid or hollow tube or pipe structure as shown in FIG. 2P.Where two, or more, tubes 220 communicate to provide translation, agroove 221 can be provided along the surface of one or bothcross-members to interlock the tubes into a cross-bar member furtherstabilizing the motion of the cross-bar relative to the implant 200. Aswill be appreciated by those of skill in the art, the cross-bar member220 can be formed integrally with the implant without departing from thescope of the invention.

As shown in FIGS. 2Q-R, it is anticipated that the surface of the tibialplateau will be prepared by forming channels thereon to receive thecross-bar members. Thus facilitating the ability of the implant to seatsecurely within the joint while still providing movement about an axiswhen the knee joint is in motion.

FIG. 2S(1-9) illustrate an alternate embodiment of implant 200. Asillustrated in FIG. 2S the edges are beveled to relax a sharp corner.FIG. 2S(1) illustrates an implant having a single fillet or bevel 230.As shown in FIG. 2S(2) two fillets 230, 231 are provided and used forthe posterior chamfer. In FIG. 2S(3) a third fillet 234 is provided tocreate two cut surfaces for the posterior chamfer. The chamfer canassist with insertion of the implant: as the implant is advanced intothe joint, the chamfer will assist with distracting the joint until theimplant is successfully seated in situ.

Turning now to FIG. 2S(4), a tangent of the implant is deselected,leaving three posterior curves. FIG. 2S(5) shows the result of tangentpropagation. FIG. 2S(6) illustrates the effect on the design when thebottom curve is selected without tangent propagation. The result oftangent propagation and selection is shown in FIG. 2S(7). As can be seenin FIG. 2S(8-9), the resulting corner has a softer edge but sacrificesless than 0.5 mm of joint space. As will be appreciated by those ofskill in the art, additional cutting planes can be added withoutdeparting from the scope of the invention.

FIGS. 2T(1-8) illustrate an alternate embodiment of an implant 200wherein the surface of the tibial plateau 250 is altered to accommodatethe implant. As illustrated in FIG. 2T(1-2), the tibial plateau can bealtered for only half of the joint surface 251 or for the full surface252. As illustrate in FIG. 2T(3-4) the posterior-anterior surface can beflat 260 or graded 262. Grading can be either positive or negativerelative to the anterior surface. Grading can also be used with respectto the implants of FIG. 2T where the grading either lies within a planeor a body or is angled relative to a plane of the body. Additionally,attachment mechanisms can be provided to anchor the implant to thealtered surface. As shown in FIG. 2T(5-7) keels 264 can be provided. Thekeels 264 can either sit within a plane, e.g. sagittal or coronal plane,or not sit within a plane (as shown in FIG. 2T(7)). FIG. 2T(8)illustrates an implant which covers the entire tibial plateau. The uppersurface of these implants are designed to conform to the projected shapeof the joint as determined under the steps described with respect toFIG. 1, while the lower surface is designed to be flat, or substantiallyflat to correspond to the modified surface of the joint.

Embodiments of the current invention provide for multiple devicesincluding implants for treating facet joints, uncovertebral joints andcostovertebral joints and methods enabling or facilitating thistreatment.

An implant can be any device or repair system for treating a facetjoint, uncovertebral joint and costovertebral or any other joint.

Distraction Device

In another embodiment of the invention, a distraction device can be usedto facilitate insertion of an implant into a facet joint. A distractiondevice can be particularly useful for placement of a balloon or aninterpositional implant into the facet joint.

In FIGS. 8A-C, for example, the distraction device can include two ormore prongs 800. One or more prongs can be straight 801 (FIG. 8A) orcurved 802 (FIG. 8B) in one or more dimensions (FIG. 8C). It can beconcave 803A with a mating concave surface 803B. The curvature can beadapted for a facet joint. It can be tapered in the front 804. It canalso be round at the tip 805. Preferably, the curvature will be similarto or substantially match that of a facet joint. One or more prongs canbe straight or curved, or partially straight and partially curved.Concave and convex shapes are possible can be present at the same time.Irregular shapes can be used.

The distraction device can include two plates at the distal tip. In FIG.9A, the plates can be substantially solid 900. The plates can also beopen on one or more sides 901 (FIG. 9B). The distraction device can havean opening 902 that allows for insertion or placement of an implant 903after distraction of the joint (FIG. 9C). Various shapes of thedistraction device 904 are possible (FIG. 9D). The distance between theplates can be substantially zero at the outset. This facilitatesinsertion into the joint. Once inserted, the distance between the platescan be increased, for example, using a telescoping or jack or ratchetlike mechanism. The distracting mechanism can be located within thejoint, preferably between the two plates, or external to the joint, forexample near the grip of the device. The two plates can be flat orcurved, or partially flat and partially curved. Preferably, thecurvature will be similar to or substantially match that of a facetjoint. Concave and convex shapes are possible can be present at the sametime. Irregular shapes can be used.

The area of the distraction device can be slightly smaller than a facetjoint, the same as the facet joint or slightly larger than a facetjoint.

The distraction device can be hollow in the center or, alternatively,create a hollow, open space to accept a balloon or an implant.

The distraction device can have an opening in the rear at the sidepointing dorsally or externally to allow insertion of the balloon orimplant while the distraction device is inside the joint.

The distal portion of the distraction device can be wider, typicallybetween two prongs, than the widest width of the implant in the samedimension, typically supero-inferior, to facilitate removal of thedistraction device with the implant remaining in situ.

Instrument to Remove or Reduce Bone Growth

Degenerated facet joints, uncovertebral joints or costovertebral jointscan demonstrate new bone formation, bone remodeling, hypertrophy, bonyovergrowth and/or bone spurs. Facet joints, uncovertebral joints orcostovertebral joints can enlarge due to new bone formation, boneremodeling, hypertrophy, bony overgrowth and/or bone spurs formation andspur formation. These conditions will be summarized in the term bonegrowth in the following.

FIGS. 3A and B demonstrate a vertebral body 300, a thecal sac 301, whichis deformed on the right side by a bone spur 308, which arises from afacet joint 303. The facet joint on the right side 303 is degenerated,while the facet joint on the left side 302 is relatively normal in shapestill. A spinous process is seen posteriorly 304. The degenerated facetjoint 303 demonstrates multiple peripheral bone spurs 306 which can leadto an enlargement of the joint. There are also irregularities of thearticular surface with some deep marks or tracks 305 and ridges or spurson the articular surface 307.

Bone growth can cause difficulties during insertion of an implant orballoon. Moreover, bone growth can cause spinal stenosis, includingforaminal stenosis, lateral recess stenosis and central stenosis. Thus,while an implant or balloon device designed to alleviate painoriginating from the affected joint, i.e., a facet joint, uncovertebraljoint or costovertebral joint, the patient may still suffer from backpain and even sciatica after the procedure. The surgeon can optionallyconsider reshaping the joint and/or removing one or more bone growths.

In one embodiment, an instrument (see 400 in FIG. 4) is used for thereshaping of the joint or the removal of one or more bone growths.

The instrument can, for example, have a ring shape at the tip 401. Theexternal aspect of the ring can be blunt 401 in order to minimizepotential damage to the thecal sac or the nerve roots. The internalportion 402 of the ring can be sharp. All or part of the externalportion can be blunt. All or part of the internal portion can be sharp.

The opening of the ring can then be placed over the bone growth and theinstrument can be pulled back, thereby removing all or part of the bonegrowth.

The instrument can include a rough surface creating a rasp-likeinstrument. In FIGS. 5A-C, various embodiments of an instrument 500 witha rough, rasp-like surface 501 are seen. The portion of the implant thatinserted into the joint 502 can have different shapes, e.g., convex orconcave in one or more planes (FIGS. 5A-5C). The instrument can have anoptional handle 503. The rough surface 501 can be moved over one or twoof the articular surfaces of the joint to remove any surfaceirregularities and to create a new, smooth bearing surface on at leastone or, optionally both sides of the joint. The underlying curvature 504of the rough surface will determine the shape of the articular surfaceafter smoothing it.

Any mechanical device or electrical mechanism capable of removing bonecan be utilized in combination with one or more of the embodiments aboveand below. For example, in FIG. 7, an instrument with a rotating mill oran oscillating saw or a shaver 700 can be utilized. This instrument canbe curved at the tip 701, thereby protecting the thecal sac 702. Theinstrument can be in a protective cover 703. The instrument is typicallyinserted via a hole in the ligamentum flavum, although it can also beinserted through the joint or both.

The distal portion of the instrument can be tapered, preferably with arounded tip. The tapered design can facilitate insertion into the jointif the instrument has to be passed through the joint. The rounded orblunt tip can help avoid injury to a nerve root or the thecal sac.

The instrument can be curved in one or more dimensions. One or moreconvex portions can be included. One or more concave portions can beincluded. Convex and concave portions can be present in the same device.

In FIGS. 6A-D, an instrument 600 is seen that has a tapered frontportion 601. The tapered front portion can be rounded 601A (FIG. 6A), ortriangular 601B (FIG. 6B). While the front of the instrument can betapered, its side portion can optionally have a sharp recess 602 (FIGS.6C and D). The sharp recess can assist in removing some bone overgrowthon or adjacent to the articular surface. The instrument can also becurved 603 near or at its tip 601 (FIG. 6D).

In a preferred embodiment, the instrument shape mirrors the shape of thearticular surface.

The instrument can be available in various sizes, thicknesses, lengthsand shapes.

In another embodiment, the instrument can have a tip that can be bentbackward in an angle equal to or greater than 90 degrees. In thissetting, the implant is passed past the bone growth. The tip is thenbrought in contact with the bone growth and the bone growth is removed.

The instrument can include one or more tubes for suction. Optionally,suction can be performed, also using standard suction devices.

The instrument to remove or reduce bone growth can be used inconjunction with the distraction device. Optionally, both can beintegrated.

Oversized Implant or Repair Device

Degenerated facet joints, uncovertebral joints or costovertebral jointscan demonstrate new bone formation, bone remodeling, hypertrophy, bonyovergrowth and/or bone spurs. Facet joints, uncovertebral joints orcostovertebral joints can enlarge due to new bone formation, boneremodeling, hypertrophy, bony overgrowth and/or bone spurs formation andspur formation. These conditions will be summarized in the term bonegrowth in the following. Bone growth can lead to an enlargement of theload bearing surface beyond the dimensions of the articular surface,i.e., portion of the joint that is covered by cartilage prior to theonset of the degenerative and arthritic changes.

Thus, an implant or a repair device including an injectable materialsized only to the articular surface, i.e., portion of the joint that iscovered by cartilage prior to the onset of the degenerative andarthritic changes, would not cover all of the load bearing surface.

In one embodiment, an implant or a repair device including a balloon oran injectable material can be oversized to account for the enlargementof the joint and the greater dimension of the load bearing surface inpatients with degenerative or arthritic changes of the facet joints,uncovertebral joints or costovertebral joints. The dimensions of theimplant or a repair device including a balloon or an injectable materialcan be increased in one or more dimensions. In addition, the shape ofthe implant can be adjusted to account for the bone growth and forirregularities in joint shape as a result of the bone growth.

In another embodiment, the implant size can be selected or adjusted toaccount for a reduction in size of the joint after removal of a bonegrowth or to account for a reduction in size of the joint after partialresection of the joint or the articular process.

These adjustments can be made intraoperatively, for example usingmeasuring or sizing devices (see below). Alternatively, theseadjustments can be made using imaging software. For example, using CT orMRI data the severity of a spinal stenosis can be estimated. In a secondstep, resection of a bone growth or partial resection of a joint orarticular process can be simulated and it can be determined what theoptimal implant size or shape is following these adjustments.

Implant Manufacturing

The implant can be patient specific with each implant custommanufactured, for example using CAD/CAM and rapid prototyping and/orcasting techniques. Alternatively, the implant can be selected from apre-existing library or assortment of implants. The library of implantswill typically cover a range of sizes and shapes applicable to mostpatients and also allowing for oversizing consistent with the embodimentabove.

Pre-Existing Repair Systems

As described herein, repair systems of various sizes, curvatures andthicknesses can be obtained. These repair systems can be catalogued andstored to create a library of systems from which an appropriate systemfor an individual patient can then be selected. In other words, adefect, or an articular surface, is assessed in a particular subject anda pre-existing repair system having a suitable shape and size isselected from the library for further manipulation (e.g., shaping) andimplantation.

Image Guidance

In various embodiments, imaging techniques can be used for delivering adevice. The imaging techniques can include the use of x-rays, CT scans,fluoroscopy, C-arms, CT fluoroscopy, C-arms with CT like cross-sectionalreconstruction and MRI. In addition to that, surgical navigationsystems, for example using radiofrequency or optical object location andreference means, can be used.

Sizing Tool

In another embodiment of the invention, a sizing tool is used todetermine the optimal shape of the implant. The sizing tool can beapplied at a first procedure, for example using percutaneous needguidance. Preferably, the sizing tool is used at the time of theprocedure for insertion of the therapeutic device into the facet joint,uncovertebral joint or costovertebral joint.

The sizing tool can include various tools for measuring implantdimensions. For example, a ruler or a caliper can be part of the sizingtool. The sizing tool can be used to measure and estimate preferreddimensions of the device, e.g., in superoinferior or mediolateraldimension. It can be used to estimate implant thickness, in one or morelocations. The sizing tool can also be used to measure implantcurvature.

In one embodiment, the sizing tool can be partially or completelydeformable. The sizing tool is inserted into the joint, thereby takingthe natural shape of the joint. The sizing tool is then withdrawn fromthe joint. The resultant shape of the sizing tool is then comparedagainst a library or assortment of premanufactured implants and the bestfitting implant with the best match relative to the sizing tool isselected.

In another embodiment, the sizing tool can include a gauge to measureimplant dimensions in antero-posterior or supero-inferior ormedio-lateral direction or combinations thereof. This gauge can, forexample, be a ruler integrated into the sizing tool. The sizing tool isinserted into the joint. The area where the dorsal portion of thearticular surface aligns with the first visible tick mark on the rulerindicates typically the preferred implant length.

The sizing tool can also include a gauge in superoinferior or any otherdimension.

One or more sizing tools can be used. The sizing tool can include one ormore dimensions of one or more of the pre-manufactured implants in theimplant library or assortment.

The sizing tool can be available in various shapes. For example, a T ort-shape can provide dimensions in two or more directions. The thicknessof the sizing tool can be used to estimate the preferred thickness ofthe implant.

Sizing tools can be made with various different curvatures and radii,typically resembling the radii of the implant. By inserting sizing toolsof different radii, the optimal radius for the implant can bedetermined.

Alternatively, the implant shape and its radii can be determined usingan imaging test.

Alternatively, a trial implant can be used. Trial implants cansubstantially match the size and shape of the implants in thepre-manufactured library of implants or assortment of implants.

The sizing tool can be malleable and/or deformable.

Preparing the Joint

In some circumstances, it may be desirable to alter the articularsurface. For example, the surgeon may elect to flatten the articularsurface, to shape it, to increase its curvature or to roughen thearticular surface or to remove the cartilage.

The shaping can be advantageous for improving the fit between theimplant and the articular surface. Roughening of the articular surfacecan improve the conformance of the implant to the articular surface andcan help reduce the risk of implant dislocation.

Facet joints are frequently rather deformed as a result of progressivedegenerative changes with deep marks and tracks distorting the articularsurface. When an interpositional implant is used, the marks and trackscan be used for stabilizing the implant on one side. The implant is thentypically made to mate with the marks and tracks on one side of thejoint thereby achieving a highly conforming surface, and, effectively, asignificant constraint to assist with reducing possible implant motionon this side of the joint. The opposing articular surface, however,needs to be minimally constraining in order to enable movement betweenthe implant surface and the opposing articular surface. Thus, theopposing surface can therefore be treated and shaped to remove any marksand tracks and to re-establish a smooth gliding surface. Preferably, theopposing surface will be made to match the smooth surface of the implanton this side.

An instrument for preparing the articular surface can be slightlysmaller than a facet, uncovertebral or costovertebral joint, similarlysized or larger in size than the respective joint.

The instrument can be curved or flat. The implant can be curved in morethan one dimension.

The instrument can be a rasp or mill-like device. It can be mechanicalor electrical in nature.

Improving Implant Stability

In most embodiments, the device shape and size is substantially matchedto one or more articular surface. The implant can fill the space betweentwo opposing articular surfaces partially or completely.

The implant can have extenders outside the articular surface forstabilizing implant position and for minimizing the risk of implantdislocation. Such an extender can be intra- or extra-articular inlocation. If it is extra-articular, it will typically extend outside thejoint capsule.

In one embodiment, the extender can be plate or disc or umbrella shaped,covering at least a portion of the bone outside the articular surface.The extender can be only partially plate or disc or umbrella shaped. Theplate or disc or umbrella shaped extender will typically be oriented atan angle to the intra-articular portion of the implant, whereby saidangle is substantially different from 180 degrees, more preferred lessthan 150 degrees, more preferred less than 120 degrees, more preferredless than 100 degrees. In some embodiments, the angle may be equal orless than 90 degrees.

The extender can have a constant or variable radii in one or moredimensions. The extender can be adapted to the patient's anatomy.

If a balloon is used and a self-hardening substance is injected into theballoon, the balloon can have a second, separate portion or a secondballoon can be attached, whereby the resultant cavity that will befilled with the self-hardening material can be located outside thearticular surface area and can be even external to the joint capsule.Once the self-hardening material is injected, the material has hardenedand the balloon has been removed, a lip or ridge or extender can becreated in this manner that can help stabilize the resultant repairdevice against the adjacent bone or soft-tissues.

Protecting Neural and Other Structures

In another embodiment of the invention, the device or implant can beshaped to protect the neural structures. For example, the ventralportion of the implant can be rounded to avoid any damage to the neuralstructures in the event the implant moves or subluxes or dislocatesanteriorly.

The dorsal and superior and inferior margins can also be rounded inorder to avoid damage to neural structures in the event of a subluxationor dislocation into the epidural space. Moreover, a round margin canhelp minimize chronic wear due to pressure onto the joint capsule.

The margin of the implant can be round along the entire implantperimeter or along a portion of the perimeter.

The implant sidewall can be straight or alternatively, it can be slantedwith an angle other than 90 degrees. The implant thickness can varyalong the perimeter.

The thickness of the implant can be thinner at the margin than in thecenter, along the entire implant margin or in portions of the implantmargin. The thickness of the implant can be thicker at the margin thanin the center, along the entire implant margin or in portions of theimplant margin.

Implant Shape for Easy Insertion

The implant shape can be adapted to facilitate insertion into the joint.For example, in FIG. 10A, the portion of the implant 1000 that will faceforward, first entering the joint, can be tapered 1001 relative toportions or all of the implant, thereby facilitating insertion. Thetapered tip can be pointed 1001 or round 1002 (FIG. 10B). In mostembodiments, a round tip is preferably since it can help reduce the riskof damage to adjacent structures.

The implant can have a sharp edge 1003 (FIG. 10C) or a rounded edge 1004(FIG. 10D). A rounded edge is typically preferred. The implant can havea substantially straight margin 1005 (FIG. 10E) or a substantiallytapered margin 1006 (FIG. 10F).

The arthroplasty can have two or more components, one essentially matingwith the tibial surface and the other substantially articulating withthe femoral component. The two components can have a flat opposingsurface. Alternatively, the opposing surface can be curved. Thecurvature can be a reflection of the tibial shape, the femoral shapeincluding during joint motion, and the meniscal shape and combinationsthereof.

Examples of single-component systems include, but are not limited to, aplastic, a polymer, a metal, a metal alloy, crystal free metals, abiologic material or combinations thereof. In certain embodiments, thesurface of the repair system facing the underlying bone can be smooth.In other embodiments, the surface of the repair system facing theunderlying bone can be porous or porous-coated. In another aspect, thesurface of the repair system facing the underlying bone is designed withone or more grooves, for example to facilitate the in-growth of thesurrounding tissue. The external surface of the device can have astep-like design, which can be advantageous for altering biomechanicalstresses. Optionally, flanges can also be added at one or more positionson the device (e.g., to prevent the repair system from rotating, tocontrol toggle and/or prevent settling into the marrow cavity). Theflanges can be part of a conical or a cylindrical design. A portion orall of the repair system facing the underlying bone can also be flatwhich can help to control depth of the implant and to prevent toggle.

Non-limiting examples of multiple-component systems include combinationsof metal, plastic, metal alloys, crystal free metals, and one or morebiological materials. One or more components of the articular surfacerepair system can be composed of a biologic material (e.g., a tissuescaffold with cells such as cartilage cells or stem cells alone orseeded within a substrate such as a bioresorable material or a tissuescaffold, allograft, autograft or combinations thereof) and/or anon-biological material (e.g., polyethylene or a chromium alloy such aschromium cobalt).

Thus, the repair system can include one or more areas of a singlematerial or a combination of materials, for example, the articularsurface repair system can have a first and a second component. The firstcomponent is typically designed to have size, thickness and curvaturesimilar to that of the cartilage tissue lost while the second componentis typically designed to have a curvature similar to the subchondralbone. In addition, the first component can have biomechanical propertiessimilar to articular cartilage, including but not limited to similarelasticity and resistance to axial loading or shear forces. The firstand the second component can consist of two different metals or metalalloys. One or more components of the system (e.g., the second portion)can be composed of a biologic material including, but not limited tobone, or a non-biologic material including, but not limited tohydroxyapatite, tantalum, a chromium alloy, chromium cobalt or othermetal alloys.

One or more regions of the articular surface repair system (e.g., theouter margin of the first portion and/or the second portion) can bebioresorbable, for example to allow the interface between the articularsurface repair system and the patient's normal cartilage, over time, tobe filled in with hyaline or fibrocartilage. Similarly, one or moreregions (e.g., the outer margin of the first portion of the articularsurface repair system and/or the second portion) can be porous. Thedegree of porosity can change throughout the porous region, linearly ornon-linearly, for where the degree of porosity will typically decreasetowards the center of the articular surface repair system. The pores canbe designed for in-growth of cartilage cells, cartilage matrix, andconnective tissue thereby achieving a smooth interface between thearticular surface repair system and the surrounding cartilage.

The repair system (e.g., the second component in multiple componentsystems) can be attached to the patient's bone with use of a cement-likematerial such as methylmethacrylate, injectable hydroxy- orcalcium-apatite materials and the like.

In certain embodiments, one or more portions of the articular surfacerepair system can be pliable or liquid or deformable at the time ofimplantation and can harden later. Hardening can occur, for example,within 1 second to 2 hours (or any time period therebetween), preferablywith in 1 second to 30 minutes (or any time period therebetween), morepreferably between 1 second and 10 minutes (or any time periodtherebetween).

FIG. 11 shows an implant device 1100 for implantation into a facet jointin accordance with one embodiment of the invention. As shown, the facetjoint includes opposing articular surfaces 1107 and 1108. In the presentembodiment, device 1100 is an interpositional device that is configuredto be inserted between opposing articular surfaces 1107 and 1108. Invarious embodiments, one side 1103 of the device 1100 forms an articularsurface in the present embodiment that is substantially smooth and thatis configured to oppose facet joint surface 1107 when implanted.Articular surface 1103 can include convex and concave shapes andcombinations thereof. Surface 1103 need not be smooth, but, preferably,the surface is configured to provide a suitable bearing surface on whichthe articular surface 1103 can glide, thereby moving relative to thesurface of the opposing articular surface 1107. Preferably, this reducesfriction between the opposing surfaces of the joint and the device andthereby reduces wear both on the device and the joint surface as well asfacilitates improved articulation of the joint surface with the device.

The opposite side 1105 of device 1100 also forms an articular surface.However, the surface 1105 substantially conforms to the correspondingjoint surface 1108. This allows surface 1105 to resist motion relativeto the opposing surface 1108, The surface 1105 incorporates the generalshape of the joint as a negative such that the surface 1105 and jointsurface 1108 couple together. By making one side of the device 1100conform with at least one articular side, the device 1100 canadvantageously be stabilized against said articular surface.

Other embodiments are possible to stabilize the device. For example, thesurface 1105 may also optionally account for irregularities caused bythe arthritis. Such an irregularity may include, without limitation,ridges, crescents, spurs, osteophytes, cysts and the like. In otherembodiments, the surface may not be specific to the joint, but mayinstead include predefined patterns of ridges, points, cones, and/orother shapes or contours, either alone or in combination, to provide asurface that resists motion. In still other embodiments, patientspecific features can be included with standardized feature. Forexample, without limitation, the articular surface of the device cangenerally match the opposing articular surface of the joint to includegeneral contours of the joint without providing a specific match ormating to the articular surface, and the standardized contours can beincluded on the surface such that the surface has a close but notperfect fit sufficient to engage the standardized resistive surfaceagainst the opposing articular surface. In another embodiment, thedevice can have a portion of the articular surface that is conformingand a portion that is not. Either or both portions can also optionallyinclude non-patient specific elements that further assist in providingstability to the device. In still other embodiments, the device caninclude an anchoring device such as a pin or fin that can be engagedwith a portion of the facet joint.

Either side 1103 or 1105 can include various combinations of one or moreconvexities and/or concavities, for example, to provide a conformingsurface or generally conforming surface. Embodiments of the device mayhave a first shape, and a second side of the implant can, optionally be,at least in part, a mirror image of said first side or said first shape.

The device 1100 may be sized to incorporate marginal and otherosteophytes. The device may also be sized and shaped to exclude suchosteophytes. The latter approach is typically preferred when theseosteophytes or spurs are removed intraoperatively. On one side thedevice can include osteophytes or bone spurs. On another side, thedevice can be shaped to exclude osteophytes.

In operation, the articular surface 1107 is able to move smoothlyrelative to surface 1103 of the device 1100. The shape of the smoothsurface 1100 as well as the opposite surface may be obtained with use ofan imaging test. The imaging test may be, without limitation, a CT orMRI, a digital tomosynthesis or methods using injection of imagingcontrast media, intra-articular or intravenous, ultrasound, or any otherimaging modality known in the art. The bony or cartilaginous landmarksmay be measured on the scan. The image may be manipulated to removeoverhanging osteophytes or other articular abnormalities virtually. Asmoothing function may be applied to the measured or derived articularsurface, for example by obtaining an image, e.g., a CT or MRI images,deriving the articular surface shape, e.g. cartilage or bone, and thenapplying a smoothing function. Alternatively, the best fittingpre-manufactured device may be selected from a library of implants.These pre-manufactured implants may already include at least one smoothbearing surface. Alternatively, the dimensions of the joint may bederived from an image, and a virtual model of an implant can be fittedto match that shape by deforming said virtual 3D model.

The device 1100 can be used unilaterally, e.g., in a left or right facetjoint, or bilaterally. The device can be used at a single spinal levelor multiple spinal levels. The device can be used in a cervical, athoracic and/or a lumbar spine.

The device 1100 may be designed to be substantially a mirror image ofthe two articular surfaces or to reflect the shape of at least onearticular surface. In various embodiments, the device 1100 may includeat least one or more convexity, concavity and/or or variation inthickness, diameter and/or general shape. Said at least one or moreconvexity, concavity and/or variation in thickness, diameter and/orgeneral shape may be designed or selected to change the spatialrelationship between the two opposing articular surfaces of the facetjoint.

In other embodiments, methods and devices for repairing facet and otherjoints allow for the customization of implants to suit a particularsubject, for example in terms of size, thickness and/or curvature. Whenthe shape (e.g., size, thickness and/or curvature) of the articularcartilage surface is an exact or near anatomic fit with the non-damagedcartilage or with the subject's original cartilage, the success ofrepair is enhanced. The repair material may be shaped prior toimplantation and such shaping can be based, for example, on electronicimages that provide information regarding curvature or thickness of any“normal” cartilage surrounding the defect and/or on curvature of thebone underlying the defect. Alternatively, an implant can includevarious combinations of both patient-specific and non-patient-specificfeatures.

Various methods may be used to manufacture both entirelypatient-specific implants as well as implants that include bothpatient-specific and non-patient specific features. For example,implants can be generated using machining, metal casting,rapid-prototyping, digital printing or other digital manufacturingmethods. Alternatively, generic implants or blanks can be manufacturedto a particular specification, and one or more patient-specificdimensions or other characteristics can be included by, for example,machining the blank to include the desired dimension or othercharacteristic or to create and entirely patient specific implant.

Thus, for example, and without limitation, a device could have astandardized smooth articular surface and a customized opposite surfacefor stabilizing the implant that is machined into the implant during themanufacturing process. Similarly, a blank implant can include standardsurfaces and be sized and/or shaped about a perimeter of the device tomatch the dimensions of the facet joints. Other embodiments may be sizedto a specific length or thickness. In still other embodiments, a set ofpatient-specific implants of varying thicknesses can be provided, forexample, in a kit or package, to allow a surgeon to select the desiredthickness during surgery to provide appropriate spacing and/or toadequately relieve pressure on the interstitial space adjacent theimplant (as discussed below).

Additionally, the implants may be manufactured using a series oftwo-dimensional (2D) and/or three-dimensional (3D) images. For example,a 3D model of the joint can be created using a set of 2D images built upin slices to provide a 3D image. In addition, to cross-sectional orvolumetric imaging technologies including CT, spiral CT, and MRI,stereoscopic imaging modalities may be utilized. Stereoscopic imaging isany technique capable of recording three-dimensional information fromtwo two-dimensional, projectional imaging. Traditional stereoscopicimaging includes creating a 3D visualization or representation startingfrom a pair of 2D images. The projection path of the 2D images isoffset. The offset is, for example, designed to create an impression ofobject depth for the eyes of the viewer. The offset or minor deviationbetween the two images is similar to the prospectors that both eyesnaturally receive in binocular vision. Using two or more images with anoffset or minor deviation in perspective, it is possible to generate apoint cloud or 3D surface or 3D visualization of a joint or an articularsurface, which can then be input into a manufacturing system such as arapid prototyping or milling machine. Dual or more light path, as wellas single light path, systems also can be employed

Software may be used to allow automatic, semi-automatic or manualidentification of relevant anatomic points to calculate the anatomic andbiomechanical parameters, in accordance with various embodiments of theinvention. Optionally, this can be done in 3D rather than only in 2D.Alternatively, the relevant anatomic points can be selected manually andthe axes can be calculated.

Identification and preparation of the implant site and insertion of theimplant also can be supported by a surgical navigation system. In such asystem, the position or orientation of a surgical instrument withrespect to the patient's anatomy can be tracked in real-time in one ormore 2D or 3D images. These 2D or 3D images can be calculated fromimages that were acquired preoperatively, such as MR or CT images.Non-image based surgical navigation systems that find axes or anatomicalstructures, for example with use of joint motion, can also be used. Theposition and orientation of the surgical instrument as well as the moldincluding alignment guides, surgical instrument guides, reaming guides,drill guides, saw guides, etc. can be determined from markers attachedto these devices. These markers can be located by a detector using, forexample, optical, acoustical or electromagnetic signals.

Referring again to FIG. 11, during an implantation procedure, thesurgeon may optionally elect intraoperatively to further smoother thearticular surface 1107. For example, a rasp or a sharp curette or anyother device known in the art may be used to modify the articularsurface.

Referring additionally to FIGS. 12-13, various embodiments are shownthat include additional features and combinations of features thatfurther stabilize the device and/or provide other benefits. For example,implant 1100 includes an anchor 1106 that serves as an anchor, stopper,cap and/or lip that engages the outer surface(s) of the facet joint toprevent the implant from sliding or otherwise moving through the jointspace or dislodging in the direction opposite anchor 1106. In apreferred embodiment, the anchor 1106 may be designed to prevent forwardsubluxation into the epidural space or into neural foramina, and reducesthe chance of or prevents potential nerve root or cord injury.

The anchor 1106 will typically be placed at the posterior facing portionof the device. The anchor 1106 may be intra-articular in location, i.e.contained within the synovial lining of the joint, or may extendexternal to the joint. The anchor may optionally be attached to thejoint capsule, e.g., with a suture or clip. The anchor 1106 may extendbeyond a joint margin or an articular surface. The anchor 1106 may beanchored against a bone spur, and/or attached to a fascia.

The anchor 1106 may be symmetrical or asymmetrical in shape. It caninclude at least one convex and/or one concave portion. The anchor 1106may be modeled to a particular patient and spinal level, for exampleusing data from a CT scan or MRI scan. All or portions of the anchor1106 can be pre-shaped or pre-manufactured to the patient's specificanatomy.

Additionally, a device 1200 may have a dumbbell-shaped ordrumstick-shaped end 1215 with a thicker portion relative to a middleportion 1216 of device 1200. (Other shapes and configurations arepossible.) As shown in FIGS. 12 and 13, in accordance with variousembodiments of the invention, the thicker portions 1215 and 1315 may belocated, without limitation, anteriorly or posteriorly, inferiorly orsuperiorly, medially or laterally. For example, thicker portion 1215 maybe about 1.5 mm, with the thinner portion 1216 being approximately 1 mm.With this device shape one articular facet, for example the inferiorfacet of the superior vertebral body, may be moved anteriorly orposteriorly. For example, by moving the inferior facet of the superiorvertebral body posteriorly, the spinal canal can be decompressed.Alternatively, by moving the superior facet of the inferior vertebralbody anteriorly, the spinal canal may be decompressed. The change indimensions of the spinal canal can be beneficial for treating stenosisinvolving at least one of a central canal, a lateral recess, a neuralforaminal space or an extraforaminal space.

The device shape may be chosen to alter the spatial relationship of thedifferent components of the facet joints favorably in order to help moveindividual portions of the facet joints and to reduce spinal stenosiscaused or aggravated by facet joint arthritis. This movement of one ormore articular surface of the facet joint may take into account bonespurs or osteophytes and help move them further away from the epiduralspace or nerve roots. Preoperative image simulation can be used tosimulate the effect of device insertion. This simulation can beperformed by simulating various types of motion, eg flexion, extension,bending, lateral bending or rotation or by simulating various types ofloading including axial loading of the spine or facet joints. In thismanner, dimensional changes on the spinal canal invoked by deviceinsertion can be assessed for different positions or differentconditions. Ultimately, this analysis can assist in identifying a deviceshape most suitable for a patient, including a device shape that isleast likely to sublux or most beneficial for changing spinal canal orforaminal dimensions.

In alternative embodiments, implants of various lengths and orthicknesses can be provided to allow a surgeon to select a device thatprovides the desired positioning of the bones of the facet joints. Instill other embodiments, an adjustable device may be provided.

Various combinations of features are possible. For example, comparingFIGS. 11 and 12, a device 1100 includes a standard end 1115 with ananchor 1106, while device 1200 includes a dumbbell-shaped end 1215 andan anchor 1206. Comparing FIGS. 12 and 13, two devices 1200 and 1300each include anchors 1206 and 1306 and dumbbell-shaped ends 1215 and1315 that are thicker relative to middle portions 1216 and 1316respectively. However, device 1200 includes two smooth articularsurfaces 1203 and 1217, while device 1300 includes one smooth articularsurface 1303 and a conforming articular surface 1317.

FIG. 14 shows a bone spur 1402 on a surface associated with a facetjoint. FIG. 15 shows a device 1500 that changes the alignment and/orposition of a facet joint, changes the dimension of the spinal canaland, optionally, pushes the spur away, in accordance with one embodimentof the invention.

The desired movement may be determined intraoperatively. Alternatively,the desired movement may be simulated preoperatively in a virtualenvironment by manipulating 2D or 3D images and objects derived fromsuch images.

Optionally, the surgeon may also elect to resect bone spurs arising froma facet joint. Preferably, the surgeon will access such bone spursthrough the facet joint without opening the anterior capsule of thefacet joint. In this manner, the epidural space remains untouched andthe possibility for bleeding and postoperative fibrosis is greatlyreduced. Spacers may also be employed in this and other embodiments.Such spacers may optionally be attached to the device and they can helpchange the spatial position of different components of the facet jointsas well.

In one embodiment of the invention, a ratchet or jack-like device can beinserted into the facet joint, optionally with a tapered tip. Theratchet or jack-like device is then used for opening the facet joint forinsertion of the device.

In a preferred embodiment, referring again to FIG. 11, the device 1100may be designed so that it can be inserted without breaching theanterior capsule of the facet joint(s) leaving the epidural spaceuntouched. This approach has the benefit of avoiding or reducingintraoperative or epidural bleeding, thereby potentially reducing theincidence of postoperative scar, fibrosis and arachnoiditis, all dreadedcomplications of spinal surgery.

If the surgeon desires to remove any bone spurs, or to smooth one ormore articular surfaces, or to resect one or more portions of the joint,she may advantageously approach the joint through a posterior approach,entering through the posterior capsule and performing these stepswithout breaching the anterior joint capsule.

Instruments may be designed for this purpose. The instruments may havesizes and shapes that substantially match the shape of the facet joints.The instruments may optionally be made individually for each patient,for example, by obtaining a pre-operative scan and then machining orrapid prototyping the instrument with a shape adapted to the joint(s) ofa particular patient. Alternatively, the instruments and/or instrumentshape can be selected based on the articular shape determined on theimaging test.

All materials known in the art can be used with the devices described inthis invention. For example, the device may be made of a metal, ceramic,and/or polymer. Non-limiting examples of metals include silver, gold,platinum, palladium, iridium, copper, tin, lead, antimony, bismuth,zinc, titanium, cobalt, stainless steel, nickel, iron alloys, cobaltalloys, such as Elgiloy®, a cobalt-chromium-nickel alloy, and MP35N, anickel-cobalt-chromium-molybdenum alloy, and Nitinol™, a nickel-titaniumalloy, aluminum, manganese, iron, tantalum, crystal free metals, such asLiquidmetal® alloys (available from LiquidMetal Technologies,www.liquidmetal.com), other metals that can slowly form polyvalent metalions, for example to inhibit calcification of implanted substrates incontact with a patient's bodily fluids or tissues, and combinationsthereof.

Nitinol can be advantageous if the device is inserted through aminimally invasive port including an endoscope. The device can then“unfold” intraoperatively and adapt to the patient's shape.

Suitable synthetic polymers include, without limitation, polyamides(e.g., nylon), polyesters, polystyrenes, polyacrylates, vinyl polymers(e.g., polyethylene, polytetrafluoroethylene, polypropylene andpolyvinyl chloride), polycarbonates, polyurethanes, poly dimethylsiloxanes, cellulose acetates, polymethyl methacrylates, polyether etherketones, ethylene vinyl acetates, polysulfones, nitrocelluloses, similarcopolymers and mixtures thereof. Bioresorbable synthetic polymers canalso be used such as dextran, hydroxyethyl starch, derivatives ofgelatin, polyvinylpyrrolidone, polyvinyl alcohol,poly[N-(2-hydroxypropyl) methacrylamide], poly(hydroxy acids),poly(epsilon-caprolactone), polylactic acid, polyglycolic acid,poly(dimethyl glycolic acid), poly(hydroxy butyrate), and similarcopolymers can also be used.

Other materials would also be appropriate, for example, the polyketoneknown as polyetheretherketone (PEEK™). This includes the material PEEK450G, which is an unfilled PEEK approved for medical implantationavailable from Victrex of Lancashire, Great Britain. (Victrex is locatedat www.matweb.com or see Boedeker www.boedeker.com). Other sources ofthis material include Gharda located in Panoli, India(www.ghardapolymers.com). Additionally, pyrolytic carbon can be used.

It should be noted that the material selected can also be filled. Forexample, other grades of PEEK are also available and contemplated, suchas 30% glass-filled or 30% carbon filled, provided such materials arecleared for use in implantable devices by the FDA, or other regulatorybody. Glass filled PEEK reduces the expansion rate and increases theflexural modulus of PEEK relative to that portion which is unfilled. Theresulting product is known to be ideal for improved strength, stiffness,or stability. Carbon filled PEEK is known to enhance the compressivestrength and stiffness of PEEK and lower its expansion rate. Carbonfilled PEEK offers wear resistance and load carrying capability.

As will be appreciated, other suitable similarly biocompatiblethermoplastic or thermoplastic polycondensate materials that resistfatigue, have good memory, are flexible, and/or deflectable have verylow moisture absorption, and good wear and/or abrasion resistance, canbe used without departing from the scope of the invention. The implantcan also be comprised of polyetherketoneketone (PEKK). Other materialsthat can be used include polyetherketone (PEK),polyetherketoneetherketoneketone (PEKEKK), andpolyetheretherketoneketone (PEEKK), and generally apolyaryletheretherketone. Further other polyketones can be used as wellas other thermoplastics.

Reference to appropriate polymers that can be used for the implant canbe made to the following documents, all of which are incorporated hereinby reference. These documents include: PCT Publication WO 02/02158 A1,dated Jan. 10, 2002 and entitled Bio-Compatible Polymeric Materials; PCTPublication WO 02/00275 A1, dated Jan. 3, 2002 and entitledBio-Compatible Polymeric Materials; and PCT Publication WO 02/00270 A1,dated Jan. 3, 2002 and entitled Bio-Compatible Polymeric Materials, eachof which is incorporated herein by reference in its entirety.

The polymers can be prepared by any of a variety of approaches includingconventional polymer processing methods. Preferred approaches include,for example, injection molding, which is suitable for the production ofpolymer components with significant structural features, and rapidprototyping approaches, such as reaction injection molding andstereo-lithography. The substrate can be textured or made porous byeither physical abrasion or chemical alteration to facilitateincorporation of the metal coating. Other processes are alsoappropriate, such as extrusion, injection, compression molding and/ormachining techniques. Typically, the polymer is chosen for its physicaland mechanical properties and is suitable for carrying and spreading thephysical load between the joint surfaces.

More than one metal, ceramic and/or polymer can be used in combination.For example, one or more metal-containing substrates can be coated withpolymers in one or more regions or, alternatively, one or morepolymer-containing substrate can be coated in one or more regions withone or more metals.

When polyethylene or other plastics are used, cross-linking techniquesknown in the art can be applied. Mild, moderate or high cross-linkingcan be used.

The system or prosthesis can be porous or porous coated. The poroussurface components can be made of various materials including metals,ceramics, and polymers. These surface components can, in turn, besecured by various means to a multitude of structural cores formed ofvarious metals. Suitable porous coatings include, but are not limitedto, metal, ceramic, polymeric (e.g., biologically neutral elastomerssuch as silicone rubber, polyethylene terephthalate and/or combinationsthereof) or combinations thereof. See, e.g., U.S. Pat. No. 3,605,123 toHahn, issued Sep. 20, 1971. U.S. Pat. No. 3,808,606 to Tronzo issued May7, 1974 and U.S. Pat. No. 3,843,975 to Tronzo issued Oct. 29, 1974; U.S.Pat. No. 3,314,420 to Smith issued Apr. 18, 1967; U.S. Pat. No.3,987,499 to Scharbach issued Oct. 26, 1976; and GermanOffenlegungsschrift 2,306,552. There can be more than one coating layerand the layers can have the same or different porosities. See, e.g.,U.S. Pat. No. 3,938,198 to Kahn, et al., issued Feb. 17, 1976.

The coating can be applied by surrounding a core with powdered polymerand heating until cured to form a coating with an internal network ofinterconnected pores. The tortuosity of the pores (e.g., a measure oflength to diameter of the paths through the pores) can be important inevaluating the probable success of such a coating in use on a prostheticdevice. See, also, U.S. Pat. No. 4,213,816 to Morris issued Jul. 22,1980. The porous coating can be applied in the form of a powder and thearticle as a whole subjected to an elevated temperature that bonds thepowder to the substrate. Selection of suitable polymers and/or powdercoatings can be determined in view of the teachings and references citedherein, for example based on the melt index of each.

Such materials include, without limitation, PEEK, pyrolytic carbone,bioresorbables (e.g., polylactic acid), metals, liquid metals, ceramics,polymers, alloys or combinations thereof.

The foregoing description of embodiments of the present invention hasbeen provided for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseforms disclosed. Many modifications and variations will be apparent tothe practitioner skilled in the art. The embodiments were chosen anddescribed in order to best explain the principles of the invention andits practical application, thereby enabling others skilled in the art tounderstand various embodiments of the invention and variousmodifications that are suited to the particular use contemplated.

1. An interpositional device for use in a facet joint, comprising: abody configured to be inserted between articular surfaces of the facetjoint, the body having first and second articular surfaces and first andsecond ends, the first articular surface having contours configured toresist motion relative to an opposing articular surface when the deviceis inserted between articular surfaces of the facet joint, the secondarticular surface configured to facilitate motion relative to anotheropposing articular surface when the device is inserted between articularsurfaces of a facet joint.
 2. The interpositional device of claim 1,wherein the first end is enlarged relative to a middle portion of thedevice.
 3. The interpositional device of claim 2, wherein the first endforms a lip configured to engage at least one surface of the facet jointand thereby resist motion of the device relative to the facet joint. 4.The interpositional device of claim 2, wherein the first end isconfigured to be located in an inter-articular position when theinterpositional device is implanted in the facet joint.
 5. Theinterpositional device of claim 2, wherein the first end is configuredto be located in an extra-articular position when the interpositionaldevice is implanted in the facet joint.
 6. The interpositional device ofclaim 1, wherein the contours of at least a portion of the firstarticular surface substantially conform to corresponding contours of theopposing articular surface.
 7. The interpositional device of claim 1,wherein at least a portion of the first articular surface substantiallyforms a negative of a corresponding portion of the opposing articularsurface.
 8. The interpositional device of claim 1, wherein the firstarticular surface is configured to secure the device when implanted inthe facet joint.
 9. The interpositional device of claim 1, wherein atleast a portion of the first articular surface is configured tointerdigitate with a corresponding portion of the opposing articularsurface when the device is implanted in the facet joint.
 10. Theinterpositional device of claim 1, wherein the second articular surfaceis substantially smooth.
 11. The interpositional device of claim 1,wherein the second end is enlarged relative to a middle portion of thedevice and is configured to enlarge a space between first and secondsurfaces of the facet joint.
 12. The interpositional device of claim 1,further comprising an attachment mechanism configured to secure thedevice in a facet joint.
 13. The interpositional device of claim 12,wherein the attachment mechanism is at least one of a pin, fin, orscrew.
 14. An patient-specific implant for use in a facet joint,comprising: a body configured to be inserted between articular surfacesof the facet joint, the body having first and second articular surfaces,at least a portion of the first articular surface substantiallyconforming to a corresponding portion of a first articular surface ofthe facet joint, the second articular surface having a substantiallysmooth portion configured to engage and move relative to a secondarticular surface of the facet joint when the implant is placed betweenthe first and second articular surfaces of the facet joint.
 15. Theimplant of claim 14, further comprising a first end and a middleportion, wherein the first end is enlarged relative to a middle portionof the device.
 16. The interpositional device of claim 15, wherein thefirst end forms a cap configured to engage at least a portion of thefacet joint and thereby resist motion of the device relative to thefacet joint.
 17. The interpositional device of claim 15, wherein thefirst end is configured to be located in an inter-articular positionwhen the interpositional device is implanted in the facet joint.
 18. Theinterpositional device of claim 15, wherein the first end is configuredto be located in an extra-articular position when the interpositionaldevice is implanted in the facet joint.
 19. The interpositional deviceof claim 14, wherein the first articular surface is configured to securethe device when implanted in the facet joint.
 20. The interpositionaldevice of claim 14, further comprising first and second ends, whereinthe first and second ends each are enlarged relative to a middle portionof the device.
 21. The interpositional device of claim 14, furthercomprising an attachment mechanism configured to secure the device in afacet joint.
 22. The interpositional device of claim 21, wherein theattachment mechanism is at least one of a pin, fin, or screw.
 23. Aninterpositional device for use in decompressing a portion of a spine,comprising: a body configured to be inserted between articular surfacesof a facet joint, the body having first and second articular surfaces, afirst end portion and a middle portion, the first articular surfaceconfigured to move relative to an opposing articular surface when thedevice is in place, the first end portion having a thickness between thefirst and second articular surfaces that is larger than a correspondingthickness of the middle portion; wherein the first end portion isconfigured to resist motion of the body relative to the facet joint inat least one direction when the interpositional device is implanted. 24.The interpositional device of claim 23, wherein at least a portion ofthe second articular surface includes contours that substantiallyconform to corresponding contours of a second articular surface.
 25. Theinterpositional device of claim 23, wherein at least a portion of thesecond articular surface substantially forms a negative of acorresponding portion of a second articular surface.
 26. Theinterpositional device of claim 23, wherein the second articular surfaceis configured to secure the device when implanted in the facet joint.27. The interpositional device of claim 23, wherein at least a portionof the second articular surface is configured to interdigitate with acorresponding portion of a second articular surface when the device isimplanted in the facet joint.
 28. The interpositional device of claim23, wherein the first articular surface is substantially smooth.
 29. Adevice for use in relieving pressure on a portion of a spine,comprising: a body configured to be inserted between articular surfacesof a facet joint, the body having first and second articular surfacesand an end portion, the first articular surface configured to engage acorresponding first surface of the facet joint when the device isimplanted, the second articular surface configured to engage acorresponding second surface of the facet joint when the device isimplanted, the end portion being relatively thicker in a directionbetween the first and second surfaces than an adjacent portion of thedevice; wherein the end portion is configured to increase the spacingbetween the first and second surfaces of the facet joint when the deviceis implanted in the facet joint.
 30. A method for decompressing aportion of a spine, comprising: inserting an implant between first andsecond articular surfaces of a facet joint to expand a space between thearticular surfaces; and stabilizing the implant in the facet joint suchthat the first and second surfaces remain in an expanded position for aperiod of time; wherein the portion of the spine decompresses as aresult of the expanded space between the articular surfaces.
 31. Themethod of claim 30, wherein pressure on an adjacent interstitial spaceof the spine is reduced.
 32. The method of claim 30, wherein painassociated with pressure on the spine is subsequently reduced.